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Large Hadron ColliderExperiments, Technology, Theory and

Future of the world's largest andhighest-energy particle accelerator

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Contents

Articles

Overview 1

CERN 1

Large Hadron Collider 11

Experiments 23

List of LHC experiments 23

ALICE 26

ATLAS 29

CMS 38

LHCb 46

LHCf 49

FP420 50

TOTEM 51

Technology 53

LHC Computing Grid 53

LHC@home 54

Proton Synchrotron Booster 55

VELO 55

Theory 56

Standard Model 56

Particle physics 69

Superpartner 75

Supersymmetry 76

Higgs boson 83

Safety 91

Safety of particle collisions at the Large Hadron Collider 91

Micro black hole 100

Strangelet 104

Future 109

Super Large Hadron Collider 109

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Very Large Hadron Collider 111

References

Article Sources and Contributors 112

Image Sources, Licenses and Contributors 115

Article Licenses

License 118

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1

Overview

CERN

European Organizationfor Nuclear Research

Organisation Européennepour la Recherche Nucléaire

Member states

Formation 29 September 1954[1]

Headquarters  Geneva, Switzerland

Membership 20 member states and 8 observers

Director General  Rolf-Dieter Heuer

Website http://www.  cern.ch/ 

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CERN 2

The 12 founding member states of CERN in 1954a[›] (map borders from 1989)

54 years after its foundation, membership to

CERN increased to 20 states, 18 of which are also

EU members as of 2008

The European Organization for Nuclear Research (French: Organisation Européenne pour la Recherche

 Nucléaire), known as CERN (see  History), pronounced / ̍sɜrn/ (French pronunciation: [sɛʁn]), is the world's largest

particle physics laboratory, situated in the northwest suburbs of Geneva on the Franco –Swiss border (46°14′3″N

6°3′19″E), established in 1954.[1] The organization has twenty European member states, and is currently the

workplace of approximately 2,600 full-time employees, as well as some 7,931 scientists and engineers (representing

580 universities and research facilities and 80 nationalities).

CERN's main function is to provide the particle accelerators and other infrastructure needed for high-energy physics

research. Numerous experiments have been constructed at CERN by international collaborations to make use of 

them. It is also noted for being the birthplace of the World Wide Web. The main site at Meyrin also has a large

computer centre containing very powerful data processing facilities primarily for experimental data analysis, and

because of the need to make them available to researchers elsewhere, has historically been (and continues to be) a

major wide area networking hub.

As an international facility, the CERN sites are officially under neither Swiss nor French jurisdiction. [2] Member

states' contributions to CERN for the year 2008 totalled CHF 1 billion (approximately € 664 million).[3]

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CERN 4

This Cisco Systems router at CERN was probably

one of the first IP routers deployed in Europe.

Prior to the Web's development, CERN had been a pioneer in the

introduction of Internet technology, beginning in the early 1980s. A

short history of this period can be found at CERN.ch [11]

More recently, CERN has become a centre for the development of Grid

computing, hosting among others the Enabling Grids for E-sciencE

(EGEE) and LHC Computing Grid projects. It also hosts the CERNInternet Exchange Point (CIXP), one of the two main Internet

Exchange Points in Switzerland. CERN's computer network is

connected to JANET (formerly UKERNA), the research and education

network, JANET aids CERN to disperse large data over a network grid

for closer analysis.

Particle accelerators

Current complex

Map of the Large Hadron Collider together with

the Super Proton Synchrotron at CERN

CERN operates a network of six accelerators and a decelerator. Each

machine in the chain increases the energy of particle beams before

delivering them to experiments or to the next more powerful

accelerator. Currently active machines are:

• Two linear accelerators generate low energy particles. Linac2

accelerates protons to 50 MeV for injection into the Proton

Synchrotron Booster (PSB), and Linac3 provides heavy ions at

4.2 MeV/u for injection into the Low Energy Ion Ring (LEIR).[12]

• The Proton Synchrotron Booster increases the energy of particles

generated by the proton linear accelerator before they are

transferred to the other accelerators.

• The Low Energy Ion Ring (LEIR) accelerates the ions from the ion

linear accelerator, before transferring them to the Proton

Synchrotron (PS). This accelerator was commissioned in 2005, after

having been reconfigured from the previous Low Energy Antiproton Ring (LEAR).

• The 28 GeV Proton Synchrotron (PS), built in 1959 and still operating as a feeder to the more powerful SPS.

• The Super Proton Synchrotron (SPS), a circular accelerator with a diameter of 2 kilometres built in a tunnel,which started operation in 1976. It was designed to deliver an energy of 300 GeV and was gradually upgraded to

450 GeV. As well as having its own beamlines for fixed-target experiments, it has been operated as a

proton –antiproton collider (the SppS collider), and for accelerating high energy electrons and positrons which

were injected into the Large Electron –Positron Collider (LEP). From 2008 onwards, it will inject protons and

heavy ions into the Large Hadron Collider (LHC).

• The On-Line Isotope Mass Separator (ISOLDE), which is used to study unstable nuclei. The radioactive ions are

produced by the impact of protons at an energy of 1.0 –1.4 GeV from the Proton Synchrotron Booster. It was first

commissioned in 1967 and was rebuilt with major upgrades in 1974 and 1992.

• REX-ISOLDE increases the charge states of ions coming from the ISOLDE targets, and accelerates them to a

maximum energy of 3 MeV/u.

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CERN 5

• The Antiproton Decelerator (AD), which reduces the velocity of antiprotons to about 10% of the speed of light for

research into antimatter.

The Large Hadron Collider

Construction of the CMS detector forLHC at CERN

Most of the activities at CERN are currently directed towards building a new

collider, the Large Hadron Collider (LHC) and the experiments for it. The LHCrepresents a large-scale, worldwide scientific cooperation project.

The LHC tunnel is located 100 metres underground, in the region between the

Geneva airport and the nearby Jura mountains. It uses the 27 km circumference

circular tunnel previously occupied by LEP which was closed down in

November 2000. CERN's existing PS/SPS accelerator complexes will be used to

pre-accelerate protons which will then be injected into the LHC.

Seven experiments (CMS, ATLAS, LHCb, MoEDAL[13] TOTEM, LHC-forward

and ALICE) will run on the collider; each of them will study particle collisions

from a different point of view, and with different technologies. Construction for

these experiments required an extraordinary engineering effort. Just as an

example, a special crane had to be rented from Belgium in order to lower pieces

of the CMS detector into its underground cavern, since each piece weighed

nearly 2,000 tons. The first of the approximately 5,000 magnets necessary for construction was lowered down a

special shaft at 13:00 GMT on 7 March 2005.

This accelerator will generate vast quantities of computer data, which CERN will stream to laboratories around the

world for distributed processing (making use of a specialised grid infrastructure, the LHC Computing Grid). In April

2005, a trial successfully streamed 600 MB/s to seven different sites across the world. If all the data generated by the

LHC is to be analysed, then scientists must achieve 1,800 MB/s before 2008.

The initial particle beams were injected into the LHC August 2008.[14] The first attempt to circulate a beam throughthe entire LHC was at 8:28 GMT on 10 September 2008,[15] but the system went wrong because of a faulty magnet

connection, and it was stopped for repairs on 19 September 2008.

The LHC resumed its operation on Friday the 20th of November 2009 by successfully circulating two beams, each

with a power of 3.5 trillion electron volts. The challenge that the engineers then faced was to try and line up the two

beams so that they smashed into each other. This is like "firing two needles across the Atlantic and getting them to

hit each other" according to the LHC's main engineer Steve Myers, director for accelerators and technology at the

Swiss laboratory.

At 1200 BST on Tuesday the 30th of March 2010 the LHC successfully smashed two proton particle beams

travelling at 3.5 TeV (trillion electron volts), with a resultant force of 7 TeV. However this is just the start of a longroad toward the expected discovery of the Higgs boson. This is mainly because the amount of data produced is so

huge it could take up to 24 months to completely analyse it all. At the end of the 7 TeV experimental period, the

LHC will be shut down for maintenance for up to a year, with the main purpose of this shut down being to strengthen

the huge magnets inside the accelerator. When it re-opens, it will attempt to create 14 TeV events.

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CERN 6

Decommissioned accelerators

• The original linear accelerator (LINAC 1).

• The 600 MeV Synchrocyclotron (SC) which started operation in 1957 and was shut down in 1991.

• The Intersecting Storage Rings (ISR), an early collider built from 1966 to 1971 and operated until 1984.

• The Large Electron –Positron Collider (LEP), which operated from 1989 to 2000 and was the largest machine of 

its kind, housed in a 27 km-long circular tunnel which now houses the Large Hadron Collider.• The Low Energy Antiproton Ring (LEAR), commissioned in 1982, which assembled the first pieces of true

antimatter, in 1995, consisting of nine atoms of antihydrogen. It was closed in 1996, and superseded by the

Antiproton Decelerator.

Sites

CERN's main site, as seen from Switzerland looking towards France.

Interior of office building 40 at the

Meyrin site. Building 40 hosts many

offices for scientists working for CMS

and Atlas.

The smaller accelerators are located on the main

Meyrin site (also known as the West Area), which was

originally built in Switzerland alongside the French

border, but has been extended to span the border since1965. The French side is under Swiss jurisdiction and

so there is no obvious border within the site, apart from

a line of marker stones. There are six entrances to the

Meyrin site:

•  A, in Switzerland. Open for all CERN personnel at

specific times.

•  B, in Switzerland. Open for all CERN personnel at

all times. Often referred to as the main entrance.

• C , in Switzerland. Open for all CERN personnel at

specific times.

•  D, in Switzerland. Open for goods reception at

specific times.

•  E , in France. Open for French-resident CERN

personnel at specific times. Controlled by customs

personnel. Named "Porte Charles de Gaulle" in

recognition of his role in the creation of the

CERN.[16]

• Tunnel entrance, in France. Open for equipment

transfer to and from CERN sites in France bypersonnel with a specific permit. This is the only

permitted route for such transfers. Under the CERN

treaty, no taxes are payable when such transfers are

made. Controlled by customs personnel.

The SPS and LEP/LHC tunnels are located

underground almost entirely outside the main site, and are mostly buried under French farmland and invisible from

the surface. However they have surface sites at various points around them, either as the location of buildings

associated with experiments or other facilities needed to operate the colliders such as cryogenic plants and access

shafts. The experiments themselves are located at the same underground level as the tunnels at these sites.

Three of these experimental sites are in France, with ATLAS in Switzerland, although some of the ancillarycryogenic and access sites are in Switzerland. The largest of the experimental sites is the Prévessin site, also known

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CERN 7

as the North Area, which is the target station for non-collider experiments on the SPS accelerator. Other sites are the

ones which were used for the UA1, UA2 and the LEP experiments (the latter which will be used for LHC

experiments).

Outside of the LEP and LHC experiments, most are officially named and numbered after the site where they were

located. For example, NA32 was an experiment looking at the production of charmed particles and located at the

Prévessin (North Area) site while WA22 used the Big European Bubble Chamber (BEBC) at the Meyrin (WestArea) site to examine neutrino interactions. The UA1 and UA2 experiments were considered to be in the

Underground Area, i.e. situated underground at sites on the SPS accelerator.

Financing (Budget 2009)

Member state Contribution Mil. CHF Mil. EUR

Germany 19.88 % 218.6 144.0

France 15.34 % 168.7 111.2

United Kingdom 14.70 % 161.6 106.5

Italy 11.51 % 126.5 83.4

Spain 8.52 % 93.7 61.8

Netherlands 4.79 % 52.7 34.7

Switzerland 3.01 % 33.1 21.8

Poland 2.85 % 31.4 20.7

Belgium 2.77 % 30.4 20.1

Sweden 2.76 % 30.4 20.0

Norway 2.53 % 27.8 18.3

Austria 2.24 % 24.7 16.3

Greece 1.96 % 20.5 13.5

Denmark 1.76 % 19.4 12.8

Finland 1.55 % 17.0 11.2

Czech Republic 1.15 % 12.7 8.4

Portugal 1.14 % 12.5 8.2

Hungary 0.78 % 8.6 5.6

Slovakia 0.54 % 5.9 3.9

Bulgaria 0.22 % 2.4 1.6

[17] Exchange rates: 1 CHF = 0,659 EUR (May 25, 2009)

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CERN 8

Member states

Member states of CERN as of 2008 Founding members  Members who joined CERN later

Animated map showing changes in CERN membership from 1954

until 1999 (borders as of 1989 and 2008)

CERN members (in blue) and observers (in red: USA, Israel, Turkey,

Japan, India, and Russia) as of 2008

The original twelve (12) CERN signatories from 1954

were:

• Belgium

• Denmark

• France

• Germany (at first only West Germany)

• Greece

• Italy

• Netherlands

• Norway

• Sweden

• Switzerland

• United Kingdom

• Yugoslavia (later withdrawn)All founding members have so far (as of 2008)

remained in the CERN organisation, except Yugoslavia

which left in 1961 and never re-joined.

Since its foundation, CERN regularly accepted new

members. All new members have remained in the

organisation continuously since their acceptance,

except Spain which joined in 1961, withdrew eight

years later, and joined anew in 1983. CERN's

membership history is as follows:

• Austria joined in 1959, bringing the total

number of members to 13.

• Yugoslavia left in 1961 (12 members)

• Spain joined in 1961 (thus increasing the

number of member states to 13 again), left in 1969

(12 members), rejoined in 1983 (13 members)

• Portugal joined in 1985 (14 member states)

• Finland joined in 1991

• Poland joined in 1991 (together with Finland

bringing the number of participating member statesto 16)

• Hungary joined in 1992 (17 members)

• Czech Republic joined in 1993

• Slovakia joined in 1993 (together with Czech

Republic increasing the total members to 19)

• Bulgaria joined in 1999 (20 member states)

There are currently twenty (20) member countries, 18

of which are also European Union member states.

• Romania became a candidate for accession toCERN in 2010 and will become the 21st member country in 2015[18]

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CERN 9

Six (6) additional countries have observer status:[19]

• Turkey - since 1961

• Israel - since 1991

• Russia - since 1993

• Japan - since 1995

• United States - since 1997• India - since 2002

Also observers are the following international organizations:

• UNESCO - since 1954

• European Commission - since 1985

Non-Member States (with dates of Co-operation Agreements) currently involved in CERN programmes are:

• Algeria

• Argentina – 11 March 1992

• Armenia – 25 March 1994

• Australia – 1 November 1991• Azerbaijan – 3 December 1997

• Belarus – 28 June 1994

• Brazil – 19 February 1990 & October 2006

• Canada – 11 October 1996

• Chile – 10 October 1991

• People's Republic of China – 12 July 1991, 14 August 1997 & 17 February 2004

• Colombia – 15 May 1993

• Croatia – 18 July 1991

• Cuba

• Cyprus – 14 February 2006• Estonia – 23 April 1996

• Georgia – 11 October 1996

• Iceland – 11 September 1996

• Iran – 5 July 2001

• Ireland

• Lithuania – 9 November 2004

• Macedonia – 27 April 2009[20]

• Mexico – 20 February 1998

• Montenegro – 12 October 1990

• Morocco – 14 April 1997• New Zealand – 4 December 2003

• Pakistan – 1 November 1994. The possibility of Pakistan becoming an Observer State has been raised on

various occasions.

• Peru – 23 February 1993

• Romania – 1 October 1991. Since 12 December 2008 it has the Status of Candidate for Accession to

Membership.

• Serbia – 8 June 2001. In 2008 it applied for accession to CERN as a Member State.[21]

• Slovenia – 7 January 1991

• South Africa – 4 July 1992

• South Korea – 25 October 2006. It might become a candidate for CERN Observer Status in a few years.• Republic of China (Taiwan)

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CERN 10

• Thailand

• Ukraine – 2 April 1993

• Vietnam

Public exhibits

The Globe of Science and Innovation at CERN

Facilities at CERN open to the public include:

• The Globe of Science and Innovation, which opened in

late 2005 and is used four times a week for special

exhibits.

• The Microcosm museum on particle physics and CERN

history.

In popular culture

• CERN is mentioned in several works of fiction and

science fiction such as Robert J. Sawyer's Flashforward 

and Dan Brown's Angels & Demons in which antimatter

figures prominently.

• CERN's Large Hadron Collider is the subject of a (scientifically accurate) rap video starring Katherine McAlpine

with some of the facility's staff.[22] [23]

• CERN is also referenced in several episodes of The Big Bang Theory - a US comedy show which frequently

references the natural sciences.

See also

• Lyn Evans, Swansea; present Project Leader of Cern• Fermilab

• Large Hadron Collider

• List of Directors General of CERN

• Science and technology in Switzerland

• SLAC

• World Wide Web

References

CERN: where the Web was born[24]

[1] CERN.ch (http://public. web. cern.ch/public/en/About/History54-en.html)[2] CERN.ch (http://dsu. web. cern. ch/dsu/ls/MissionE.htm)

[3] CERN Website - Resources Planning and Control (http://dg-rpc.web.cern. ch/ 

dg-rpc/Scale. html)

[4] The CERN Name (http://public. web. cern.ch/Public/Content/Chapters/ 

AboutCERN/WhatIsCERN/CERNName/CERNName-en.html), on the CERN

website. Last accessed on 25 October 2006.

[5] CERN.ch (http://public. web. cern.ch/public/en/About/History73-en.html)

[6] CERN.ch (http://public. web. cern.ch/public/en/About/History83-en.html)

[7] CERN.ch (http://public. web. cern.ch/public/en/About/History95-en.html)

[8] V. Fanti et al., Phys. Lett. B465 (1999) 335 (hep-ex/9909022) (http://arxiv.  org/ 

abs/hep-ex/9909022v1)

[9] CERN.ch (http://public. 

web. 

cern.ch/Public/en/About/WebStory-en.html)[10] W3.org (http://www. w3. org/History/19921103-hypertext/hypertext/WWW/TheProject. html)

[11] CERN.ch (http://www. cern.ch/ben/TCPHIST.  html)

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CERN 11

[12] CERN Website - LINAC (http://linac2.home.cern.ch/linac2/default. htm)

[13] CERN Courier, "MoEDAL becomes the LHC's magnificent seventh" (http://cerncourier. com/cws/article/cern/42329), May 5th 2010

[14] Overbye, Dennis (29 July 2008). " Let the Proton Smashing Begin. (The Rap Is Already Written.) (http://www.  nytimes. com/2008/07/ 

29/science/29cernrap. html)". The New York Times.

[15] CERN press release, 7 August 2008 (http://press.web. cern. ch/press/PressReleases/Releases2008/PR06. 08E.  html)

[16] " Red Carpet for CERN's 50th (http://bulletin.cern.ch/eng/articles.  php?bullno=45/2004&base=art)".CERN bulletin. November 2004.

[17] CERN.ch (http://dg-rpc. web. cern. ch/dg-rpc/Budget/Budget09. pdf)

[18] CERN.ch (http://public. web.cern.ch/public/)[19] "ISAAR relationship data at CERN library" (http://library.  web.cern.ch/library/Archives/archnet/isaarcern.  html). . Retrieved

2009-12-14.

[20]  Macedonia joins CERN (SUP) (http://www.mia.  com.  mk/default. aspx?mId=1&vId=64153836&lId=2&title=MACEDONIA+-+

INTERNAL+AFFAIRS+)

[21] Djelic to meet CERN Director General (http://www. emportal.rs/en/news/serbia/87520. html)

[22] Youtube.com (http://www. youtube.com/watch?v=j50ZssEojtM)

[23] "Large Hadron Collider Rap Video Is a Hit" (http://news.nationalgeographic.com/news/2008/09/080910-odd-particl-AP. html),

National Geographic News. September 10, 2008. Retrieved August 13, 2010.

[24] Plaque #2196 on Open Plaques (http://openplaques.org/plaques/2196).

External links

• Official website (http://www.cern.ch)

• CERN at 50 (http://www.economist.  com/science/PrinterFriendly. cfm?Story_ID=2535917)

• CERN Courier - International journal of high-energy physics (http://cerncourier. com)

• CERN chronology (http://library. cern.ch/archives/chrono/chrono_2002_cern.  php)

Geographical coordinates: 46°14′03″N 6°03′10″E

Large Hadron Collider

Geographical coordinates: 46°14′N 06°03′E

LHC experiments

ATLAS A Toroidal LHC Apparatus

CMS Compact Muon Solenoid

LHCb LHC-beauty

ALICE A Large Ion Collider Experiment

TOTEM Total Cross Section, Elastic Scattering and Diffraction Dissociation

LHCf  LHC-forward

MoEDAL Monopole and Exotics Detector At the LHC

LHC preaccelerators

p and Pb Linear accelerators for protons (Linac 2) and Lead (Linac 3)

(not marked) Proton Synchrotron Booster

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Large Hadron Collider 12

PS Proton Synchrotron

SPS Super Proton Synchrotron

Intersecting Storage Rings CERN, 1971 –1984

Super Proton Synchrotron CERN, 1981 –1984

ISABELLE BNL, cancelled in 1983

Tevatron Fermilab, 1987 –present

Relativistic Heavy Ion Collider BNL, 2000 –present

Superconducting Super Collider Cancelled in 1993

Large Hadron Collider CERN, 2009 –present

Super Large Hadron Collider Proposed, CERN, 2019 –

Very Large Hadron Collider Theoretical

The Large Hadron Collider (LHC) is the world's largest and highest-energy particle accelerator. It is expected that

it will address the most fundamental questions of physics, advancing our understanding of the deepest laws of nature.

The LHC lies in a tunnel 27 kilometres (17 mi) in circumference, as much as 175 metres (574 ft) beneath the

Franco-Swiss border near Geneva, Switzerland. This synchrotron is designed to collide opposing particle beams of 

either protons at an energy of 7 teraelectronvolts (1.12 microjoules) per particle, or lead nuclei at an energy of 

574 TeV (92.0 µJ) per nucleus.[1] [2] The term hadron refers to particles composed of quarks.

The Large Hadron Collider was built by the European Organization for Nuclear Research (CERN) with the intention

of testing various predictions of high-energy physics, including the existence of the hypothesized Higgs boson[3] and

of the large family of new particles predicted by supersymmetry.[4] It is funded by and built in collaboration with

over 10,000 scientists and engineers from over 100 countries as well as hundreds of universities and laboratories.[5]

On 10 September 2008, the proton beams were successfully circulated in the main ring of the LHC for the firsttime,[6] but 9 days later operations were halted due to a serious fault.[7] On 20 November 2009 they were

successfully circulated again,[8] with the first proton –proton collisions being recorded 3 days later at the injection

energy of 450 GeV per beam.[9] After the 2009 winter shutdown, the LHC was restarted and the beam was ramped

up to 3.5 TeV per beam,[10] half its designed energy,[11] which is planned for after its 2012 shutdown. On 30 March

2010, the first planned collisions took place between two 3.5 TeV beams, which set a new world record for the

highest-energy man-made particle collisions.[12]

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Large Hadron Collider 13

Purpose

A simulated event in the CMS detector, featuring

the appearance of the Higgs boson

Physicists hope that the LHC will help answer many of the most

fundamental questions in physics: questions concerning the basic laws

governing the interactions and forces among the elementary objects,

the deep structure of space and time, especially regarding the

intersection of quantum mechanics and general relativity, wherecurrent theories and knowledge are unclear or break down altogether.

These issues include, at least:[13]

• Is the Higgs mechanism for generating elementary particle masses

via electroweak symmetry breaking indeed realised in nature?[14] It

is anticipated that the collider will either demonstrate or rule out the

existence of the elusive Higgs boson(s), completing (or refuting) the

Standard Model.[15] [16] [17]

• Is supersymmetry, an extension of the Standard Model and Poincaré

symmetry, realised in nature, implying that all known particles have supersymmetric partners?[18]

 [19]

 [20]

• Are there extra dimensions,[21] as predicted by various models inspired by string theory, and can we detect

them?[22]

• What is the nature of the Dark Matter which appears to account for 23% of the mass of the Universe?

Other questions are:

• Are electromagnetism, the strong nuclear force and the weak nuclear force just different manifestations of a single

unified force, as predicted by various Grand Unification Theories?

• Why is gravity so many orders of magnitude weaker than the other three fundamental forces? See also Hierarchy

problem.

• Are there additional sources of quark flavours, beyond those already predicted within the Standard Model?

• Why are there apparent violations of the symmetry between matter and antimatter? See also CP violation.

• What was the nature of the quark-gluon plasma in the early universe? This will be investigated by heavy ion

collisions in ALICE.

Design

A Feynman diagram of one way the Higgs boson

may be produced at the LHC. Here, two quarks

each emit a W or Z boson, which combine to

make a neutral Higgs.

The LHC is the world's largest and highest-energy particle

accelerator.[1] [23] The collider is contained in a circular tunnel, with a

circumference of 27 kilometres (17 mi), at a depth ranging from 50 to

175 metres (160 to 574 ft) underground.

The 3.8-metre (12 ft) wide concrete-lined tunnel, constructed between

1983 and 1988, was formerly used to house the Large

Electron –Positron Collider.[24] It crosses the border between

Switzerland and France at four points, with most of it in France.

Surface buildings hold ancillary equipment such as compressors,

ventilation equipment, control electronics and refrigeration plants.

The collider tunnel contains two adjacent parallel beam pipes that

intersect at four points, each containing a proton beam, which travel in

opposite directions around the ring. Some 1,232 dipole magnets keep

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Large Hadron Collider 14

Map of the Large Hadron Collider at CERN

the beams on their circular path, while an additional 392 quadrupole

magnets are used to keep the beams focused, in order to maximize the

chances of interaction between the particles in the four intersection

points, where the two beams will cross. In total, over 1,600

superconducting magnets are installed, with most weighing over 27

tonnes. Approximately 96 tonnes of liquid helium is needed to keep themagnets at their operating temperature of 1.9 K (−271.25 °C), making

the LHC the largest cryogenic facility in the world at liquid helium

temperature.

Superconducting quadrupole electromagnets are

used to direct the beams to four intersection

points, where interactions between accelerated

protons will take place.

Once or twice a day, as the protons are accelerated from 450 GeV to

7 TeV, the field of the superconducting dipole magnets will beincreased from 0.54 to 8.3 teslas (T). The protons will each have an

energy of 7 TeV, giving a total collision energy of 14 TeV. At this

energy the protons have a Lorentz factor of about 7,500 and move at

about 0.999999991 c, or about 3 metres per second slower than the

speed of light (c).[25] It will take less than 90 microseconds (μs) for a

proton to travel once around the main ring – a speed of about 11,000

revolutions per second. Rather than continuous beams, the protons will

be bunched together, into 2,808 bunches, so that interactions between

the two beams will take place at discrete intervals never shorter than 25

nanoseconds (ns) apart. However it will be operated with fewerbunches when it is first commissioned, giving it a bunch crossing

interval of 75 ns.[26] The design luminosity of the LHC is 1034 cm-2s-1, providing a bunch collision rate of 40 MHz.[27]

Prior to being injected into the main accelerator, the particles are prepared by a series of systems that successively

increase their energy. The first system is the linear particle accelerator LINAC 2 generating 50-MeV protons, which

feeds the Proton Synchrotron Booster (PSB). There the protons are accelerated to 1.4 GeV and injected into the

Proton Synchrotron (PS), where they are accelerated to 26 GeV. Finally the Super Proton Synchrotron (SPS) is used

to further increase their energy to 450 GeV before they are at last injected (over a period of 20 minutes) into the

main ring. Here the proton bunches are accumulated, accelerated (over a period of 20 minutes) to their peak 7-TeV

energy, and finally circulated for 10 to 24 hours while collisions occur at the four intersection points.[28]

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Large Hadron Collider 15

CMS detector for LHC

The LHC physics program is mainly based on proton –proton collisions.

However, shorter running periods, typically one month per year, with heavy-ion

collisions are included in the program. While lighter ions are considered as well,

the baseline scheme deals with lead ions[29] (see A Large Ion Collider

Experiment). The lead ions will be first accelerated by the linear accelerator

LINAC 3, and the Low-Energy Ion Ring (LEIR) will be used as an ion storageand cooler unit. The ions will then be further accelerated by the PS and SPS

before being injected into LHC ring, where they will reach an energy of 2.76

TeV per nucleon (or 575 TeV per ion), higher than the energies reached by the

Relativistic Heavy Ion Collider. The aim of the heavy-ion program is to

investigate quark –gluon plasma, which existed in the early universe.

DetectorsSix detectors have been constructed at the LHC, located underground in large caverns excavated at the LHC's

intersection points. Two of them, the ATLAS experiment and the Compact Muon Solenoid (CMS), are large, general

purpose particle detectors.[23] A Large Ion Collider Experiment (ALICE) and LHCb, have more specific roles and

the last two, TOTEM and LHCf, are very much smaller and are for very specialized research. The BBC's summary

of the main detectors is:[30]

Detector Description

ATLAS one of two general purpose detectors. ATLAS will be used to look for signs of new physics, including the origins of mass and extra

dimensions.

CMS the other general purpose detector will, like ATLAS, hunt for the Higgs boson and look for clues to the nature of dark matter.

ALICE will study a "liquid" form of matter called quark –gluon plasma that existed shortly after the Big Bang.

LHCb equal amounts of matter and antimatter were created in the Big Bang. LHCb will try to investigate what happened to the "missing"

antimatter.

Operational timeline

The first beam was circulated through the collider on the morning of 10 September 2008.[30] CERN successfully

fired the protons around the tunnel in stages, three kilometres at a time. The particles were fired in a clockwise

direction into the accelerator and successfully steered around it at 10:28 local time.[31]

The LHC successfullycompleted its first major test: after a series of trial runs, two white dots flashed on a computer screen showing the

protons travelled the full length of the collider. It took less than one hour to guide the stream of particles around its

inaugural circuit.[32] CERN next successfully sent a beam of protons in a counterclockwise direction, taking slightly

longer at one and a half hours due to a problem with the cryogenics, with the full circuit being completed at 14:59. In

the original timeline of the LHC commissioning, the first "modest" high-energy collisions at a center-of-mass energy

of 900 GeV were expected to take place before the end of September 2008, and the LHC was expected to be

operating at 10 TeV by the time of the official inauguration on 21 October 2008.[33] However, due to the delay

caused by the above-mentioned incident, the collider was not operational until November 2009.[34] Despite the

delay, LHC was officially inaugurated on 21 October 2008, in the presence of political leaders, science ministers

from CERN's 20 Member States, CERN officials, and members of the worldwide scientific community.[35] CERNscientists estimate that if the Standard Model is correct, a single Higgs boson may be produced every few hours. At

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Large Hadron Collider 16

this rate, it may take about two to three years to collect enough data to discover the Higgs boson unambiguously.

Similarly, it may take one year or more before sufficient results concerning supersymmetric particles have been

gathered to draw meaningful conclusions.[1]

On 19 September 2008, a quench occurred in about 100 bending magnets in sectors 3 and 4, causing a loss of 

approximately six tonnes of liquid helium, which was vented into the tunnel, and a temperature rise of about 100

kelvin in some of the affected magnets. Vacuum conditions in the beam pipe were also lost.[36]

Shortly after theincident CERN reported that the most likely cause of the problem was a faulty electrical connection between two

magnets, and that – due to the time needed to warm up the affected sectors and then cool them back down to

operating temperature – it would take at least two months to fix it.[37] Subsequently, CERN released a preliminary

analysis of the incident on 16 October 2008,[38] and a more detailed one on 5 December 2008.[39] Both analyses

confirmed that the incident was indeed initiated by a faulty electrical connection. A total of 53 magnets were

damaged in the incident and were repaired or replaced during the winter shutdown.[40]

Most of 2009 was spent on repairs and reviews from the damage caused by the quench incident. On November 20,

the first low-energy beams circulated in the tunnel for the first time since the incident. On December 15, 2009, the

first physics results from the LHC were reported, involving 284 collisions that took place in the ALICE detector.[41]

The early part of 2010 saw the continue ramp-up of beam in energies and early physic experiments. The results of the first proton –proton collisions at energies higher than Fermilab's Tevatron proton –antiproton collisions have been

published, yielding greater-than-predicted charged hadron production.[42] The CMS paper reports that the increase in

the production rate of charged hadrons when the center-of-mass energy goes from 0.9 TeV to 2.36 TeV exceeds the

predictions of the theoretical models used in the analysis, with the excess ranging from 10% to 14%, depending upon

which model is used. The charged hadrons were primarily mesons (kaons and pions).[43] On 30 March 2010, LHC

set a record for high-energy collisions, by colliding proton beams at a combined energy level of 7 TeV. The attempt

was the third that day, after two unsuccessful attempts in which the protons had to be "dumped" from the collider

and new beams had to be injected.[44] CERN has declared a schedule to operate the LHC through the rest of 2010

and most of 2011 before the next scheduled shutdown.[45]

Timeline

Date Event

10 Sep 2008 CERN successfully fired the first protons around the entire tunnel circuit in stages.

19 Sep 2008 Magnetic quench occurred in about 100 bending magnets in sectors 3 and 4, causing a loss of approximately 6 tonnes of liquid

helium.

30 Sep 2008 First "modest" high-energy collisions planned but postponed due to accident.

16 Oct 2008 CERN released a preliminary analysis of the incident.

21 Oct 2008 Official inauguration.5 Dec 2008 CERN released detailed analysis.

20 Nov 2009 Low-energy beams circulated in the tunnel for the first time since the incident.[46]

23 Nov 2009 First particle collisions in all four detectors at 450 GeV.[9]

30 Nov 2009 LHC becomes the world's highest-energy particle accelerator achieving 1.18 TeV per beam, beating the Tevatron's previous record of 

0.98 TeV per beam held for eight years.[47]

28 Feb 2010 The LHC continues operations ramping energies to run at 3.5 TeV for 18 months to two years, after which it will be shut down to

prepare for the 14 TeV collisions (7 TeV per beam).[48]

30 Mar 2010 The two beams collided at 7 TeV (3.5 TeV per beam) in the LHC at 13:06 CEST, marking the start of the LHC research program.

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Large Hadron Collider 17

Proposed upgrade

After some years of running, any particle physics experiment typically begins to suffer from diminishing returns:

each additional year of operation discovers less than the year before. The way around the diminishing returns is to

upgrade the experiment, either in energy or in luminosity. A luminosity upgrade of the LHC, called the Super LHC,

has been proposed,[49] to be made after ten years of LHC operation.

The optimal path for the LHC luminosity upgrade includes an increase in the beam current (i.e., the number of protons in the beams) and the modification of the two high-luminosity interaction regions, ATLAS and CMS. To

achieve these increases, the energy of the beams at the point that they are injected into the (Super) LHC should also

be increased to 1 TeV. This will require an upgrade of the full pre-injector system, the needed changes in the Super

Proton Synchrotron being the most expensive.

Cost

With a budget of 9 billion US dollars (approx. €7.5bn or £6.19bn as of Jun 2010), the LHC is one of the most

expensive scientific instruments[50] ever built.[51] The total cost of the project is expected to be of the order of 4.6bn

Swiss francs (approx. $4.4bn, €3.1bn, or £2.8bn as of Jan 2010) for the accelerator and SFr 1.16bn (approx. $1.1bn,€0.8bn, or £0.7bn as of Jan 2010) for the CERN contribution to the experiments.[52]

The construction of LHC was approved in 1995 with a budget of SFr 2.6bn, with another SFr 210M towards the

experiments. However, cost overruns, estimated in a major review in 2001 at around SFr 480M for the accelerator,

and SFr 50M for the experiments, along with a reduction in CERN's budget, pushed the completion date from 2005

to April 2007.[53] The superconducting magnets were responsible for SFr 180M of the cost increase. There were also

further costs and delays due to engineering difficulties encountered while building the underground cavern for the

Compact Muon Solenoid,[54] and also due to faulty parts provided by Fermilab.[55] Due to lower electricity costs

during the summer, it is expected that the LHC will normally not operate over the winter months, [56] although an

exception was made to make up for the 2008 start-up delays over the 2009/10 winter.

Computing resources

Data produced by LHC as well as LHC-related simulation will produce a total data output of 15 petabytes per year

(max throughput while running not stated).[57]

The LHC Computing Grid is being constructed to handle the massive amounts of data produced. It incorporates both

private fiber optic cable links and existing high-speed portions of the public Internet, enabling data transfer from

CERN to academic institutions around the world.

The Open Science Grid is used as the primary infrastructure in the United States, and also as part of an interoperable

federation with the LHC Computing Grid.

The distributed computing project LHC@home was started to support the construction and calibration of the LHC.

The project uses the BOINC platform, enabling anybody with an internet connection to use their computer idle time

to simulate how particles will travel in the tunnel. With this information, the scientists will be able to determine how

the magnets should be calibrated to gain the most stable "orbit" of the beams in the ring.

Safety of particle collisions

The experiments at the Large Hadron Collider sparked fears among the public that the particle collisions might

produce doomsday phenomena, involving the production of stable microscopic black holes or the creation of 

hypothetical particles called strangelets.[58] Two CERN-commissioned safety reviews examined these concerns and

concluded that the experiments at the LHC present no danger and that there is no reason for concern,[59] [60] [61] aconclusion expressly endorsed by the American Physical Society.[62]

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Large Hadron Collider 18

Operational challenges

The size of the LHC constitutes an exceptional engineering challenge with unique operational issues on account of 

the amount of energy stored in the magnets and the beams.[28]  [63] While operating, the total energy stored in the

magnets is 10 GJ (equivalent to 2.4 tons of TNT) and the total energy carried by the two beams reaches 724 MJ (173

kilograms of TNT).[64]

Loss of only one ten-millionth part (10−7) of the beam is sufficient to quench a superconducting magnet, while thebeam dump must absorb 362 MJ (87 kilograms of TNT) for each of the two beams. These energies are carried by

very little matter: under nominal operating conditions (2,808 bunches per beam, 1.15×10 11 protons per bunch), the

beam pipes contain 1.0×10−9 gram of hydrogen, which, in standard conditions for temperature and pressure, would

fill the volume of one grain of fine sand.

Construction accidents and delays

• On 25 October 2005, José Pereira Lages, a technician, was killed in the LHC when a switchgear that was being

transported fell on him.[65]

• On 27 March 2007 a cryogenic magnet support broke during a pressure test involving one of the LHC's innertriplet (focusing quadrupole) magnet assemblies, provided by Fermilab and KEK. No one was injured. Fermilab

director Pier Oddone stated "In this case we are dumbfounded that we missed some very simple balance of 

forces". This fault had been present in the original design, and remained during four engineering reviews over the

following years.[66] Analysis revealed that its design, made as thin as possible for better insulation, was not strong

enough to withstand the forces generated during pressure testing. Details are available in a statement from

Fermilab, with which CERN is in agreement.[67] [68] Repairing the broken magnet and reinforcing the eight

identical assemblies used by LHC delayed the startup date, then planned for November 2007.

• Problems occurred on 19 September 2008 during powering tests of the main dipole circuit, when an electrical

fault in the bus between magnets caused a rupture and a leak of six tonnes of liquid helium. The operation was

delayed for several months.[69]

It is currently believed that a faulty electrical connection between two magnetscaused an arc, which compromised the liquid-helium containment. Once the cooling layer was broken, the helium

flooded the surrounding vacuum layer with sufficient force to break 10-ton magnets from their mountings. The

explosion also contaminated the proton tubes with soot.[39] [70] This accident was more recently thoroughly

discussed in a 22 February 2010 Superconductor Science and Technology article by CERN physicist Lucio

Rossi.[71]

• Two vacuum leaks were identified in July 2009, and the start of operations was further postponed to

mid-November 2009.[72]

Popular culture

The Large Hadron Collider has gained considerable attention from outside the scientific community and its progress

is followed by most popular science media. The LHC has also sparked the imaginations of authors of works of 

fiction, such as novels, TV series, and video games, although descriptions of what it is, how it works, and projected

outcomes of the experiments are often only vaguely accurate, occasionally causing concern among the general

public.

The novel Angels & Demons, by Dan Brown, involves antimatter created at the LHC to be used in a weapon against

the Vatican. In response CERN published a "Fact or Fiction?" page discussing the accuracy of the book's portrayal of 

the LHC, CERN, and particle physics in general.[73] The movie version of the book has footage filmed on-site at one

of the experiments at the LHC; the director, Ron Howard, met with CERN experts in an effort to make the science in

the story more accurate.[74]

In The Big Bang Theory, the episode The Large Hadron Collision features the Large Hadron Collider prominently.

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Large Hadron Collider 19

The novel  FlashForward , by Robert J. Sawyer, involves the search for the Higgs boson at the LHC. CERN

published a "Science and Fiction" page interviewing Sawyer and physicists about the book and the TV series based

on it.[75]

CERN employee Katherine McAlpine's "Large Hadron Rap" [76][77] surpassed 6 million YouTube views.[78] [79]

The band Les Horribles Cernettes was founded by female members of CERN. The name was chosen so to have the

same initials as the LHC.[80]

 [81]

They are the first band to have a site on the World Wide Web,[82]

and their photothere was the first to ever appear on the Web.[83]

See also

• International Linear Collider

• List of accelerators in particle physics

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php3?id_article=22468&ei=qIs-TPDAC8G88gaV7NmhBA&sa=X&oi=translate&ct=result&resnum=1&ved=0CBgQ7gEwAA&prev=/ 

search?q=http://www. lienmultimedia.com/article.php3%3Fid_article%3D22468&hl=en&client=firefox-a&hs=yCb&rls=org.

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Large Hadron Collider 21

mozilla:en-US:official)

[52] "How much does it cost?" (http://askanexpert. web.cern.ch/AskAnExpert/en/Accelerators/LHCgeneral-en. html#3). CERN. 2007. .

Retrieved 2009-09-28.

[53] Luciano Maiani (16 October 2001). "LHC Cost Review to Completion" (http://user.  web. cern. ch/User/LHCCost/2001-10-16/ 

LHCCostReview. html). CERN. . Retrieved 2001-01-15.

[54] Toni Feder (2001). "CERN Grapples with LHC Cost Hike" (http://ptonline.aip.org/journals/doc/PHTOAD-ft/vol_54/iss_12/21_2.

shtml). Physics Today  54 (12): 21. doi:10.1063/1.1445534. .

[55] "Bursting magnets may delay CERN collider project" (http://www.reuters.com/article/scienceNews/idUSL054919720070405). Reuters.5 April 2007. . Retrieved 2009-09-28.

[56] Paul Rincon (23 September 2008). "Collider halted until next year" (http://news.  bbc. co. uk/1/hi/sci/tech/7632408. stm). BBC News. .

Retrieved 2009-09-28.

[57] "CERN LHC Computing" (http://public. web.cern.ch/public/en/LHC/Computing-en. html). CERN. 2008. . Retrieved 2009-09-28.

[58] Alan Boyle (2 September 2008). "Courts weigh doomsday claims" (http://cosmiclog. msnbc.  msn.  com/archive/2008/09/02/1326534.

aspx). Cosmic Log. MSNBC. . Retrieved 2009-09-28.

[59] J.-P. Blaizot, J. Iliopoulos, J. Madsen, G.G. Ross, P. Sonderegger, H.-J. Specht (2003). "Study of Potentially Dangerous Events During

Heavy-Ion Collisions at the LHC" (http://doc.cern.ch/yellowrep/2003/2003-001/p1.  pdf). CERN. . Retrieved 2009-09-28.

[60] J. Ellis J, G. Giudice, M.L. Mangano, T. Tkachev, U. Wiedemann (LHC Safety Assessment Group) (5 September 2008). "Review of the

Safety of LHC Collisions". Journal of Physics G 35: 115004. doi:10.1088/0954-3899/35/11/115004. arXiv:0806.3414.

[61] "The safety of the LHC" (http://public. web. cern.ch/public/en/LHC/Safety-en.  html). CERN. 2008. . Retrieved 2009-09-28.

[62] Division of Particles & Fields (http://www.aps.org/units/dpf/). "Statement by the Executive Committee of the DPF on the Safety of Collisions at the Large Hadron Collider" (http://www.aps.org/units/dpf/governance/reports/upload/lhc_saftey_statement. pdf). American

Physical Society. . Retrieved 2009-09-28.

[63] "Challenges in accelerator physics" (http://lhc.web. cern.ch/lhc/general/acphys.htm). CERN. 14 January 1999. . Retrieved 2009-09-28.

[64] John Poole (2004). "Beam Parameters and Definitions" (https://edms.cern.ch/file/445830/5/Vol_1_Chapter_2. pdf). .

[65] CERN Press Office (26 October 2005). "Message from the Director-General" (http://user.  web. cern. ch/user/QuickLinks/ 

Announcements/2005/Accident.html). Press release. . Retrieved 2009-09-28.

[66] "Fermilab 'Dumbfounded' by fiasco that broke magnet" (http://www.  photonics. com/content/news/2007/April/4/87089. aspx).

Photonics.com. 4 April 2007. . Retrieved 2009-09-28.

[67] CERN Press Office (1 June 2007). "Fermilab update on inner triplet magnets at LHC: Magnet repairs underway at CERN" (http://user.

web. cern. ch/user/QuickLinks/Announcements/2007/LHCInnerTriplet_5. html). Press release. . Retrieved 2009-09-28.

[68] "Updates on LHC inner triplet failure" (http://www. fnal. gov/pub/today/lhc_magnet_archive. html). Fermilab Today . Fermilab. 28

September 2007. . Retrieved 2009-09-28.

[69] Paul Rincon (23 September 2008). "Collider halted until next year" (http://news.  bbc. co. uk/2/hi/in_depth/7632408. stm). BBC News. .

Retrieved 2009-09-29.

[70] Dennis Overbye (5 December 2008). "After repairs, summer start-up planned for collider" (http://www. nytimes. com/2008/12/06/ 

science/06cern. html). New York Times. . Retrieved 2008-12-08.

[71] http://www. iop.  org/EJ/article/0953-2048/23/3/034001/sust10_3_034001. pdf?request-id=70c5f5ed-6913-4a93-a944-14f91f848c14

[72] "News on the LHC" (http://user.web.cern.ch/user/news/2009/090716. html). CERN. 16 July 2009. . Retrieved 2009-09-28.

[73] "Angels and Demons" (http://public.web.cern. ch/Public/en/Spotlight/SpotlightAandD-en. html). CERN. January 2008. . Retrieved

2009-09-28.

[74] Ceri Perkins (2 June 2008). "ATLAS gets the Hollywood treatment" (http://atlas-service-enews. web. cern. ch/atlas-service-enews/news/ 

news_angelphoto. php). ATLAS e-News. . Retrieved 2009-09-28.

[75] "FlashForward" (http://flashforward. web.cern.ch/flashforward/). CERN. September 2009. . Retrieved 2009-10-03.

[76] http://www. youtube.  com/watch?v=j50ZssEojtM

[77] Katherine McAlpine (28 July 2008). "Large Hadron Rap" (http://www. 

youtube.com/watch?v=j50ZssEojtM). YouTube. . Retrieved2009-09-28.

[78] Roger Highfield (6 September 2008). "Rap about world's largest science experiment becomes YouTube hit" (http://www.  telegraph. co. uk/ 

earth/main.  jhtml?xml=/earth/2008/08/26/scirap126. xml). Telegraph (London). . Retrieved 2009-09-28.

[79] Jennifer Bogo (1 August 2008). "Large Hadron Collider rap teaches particle physics in 4 minutes" (http://www. popularmechanics. com/ 

blogs/science_news/4276090.html). Popular Mechanics . . Retrieved 2009-09-28.

[80] Malcolm W Brown (1998-12-29). "Physicists Discover Another Unifying Force: Doo-Wop" (http://musiclub. web. cern. ch/MusiClub/ 

bands/cernettes/Press/NYT. pdf). New York Times (New York, USA). . Retrieved 2010-09-21.

[81] Heather McCabe (Feb 10 1999). "Grrl Geeks Rock Out" (http://musiclub.web. cern. ch/MusiClub/bands/cernettes/Press/Wired. pdf).

Wired News. . Retrieved 2010-09-21.

[82] James Gillies (6 September 2008). "Making a song and dance about physics" (http://cerncourier. com/cws/article/cern/27907). CERN 

Courier (CERN). . Retrieved 2010-09-24.

[83] Silvano de Gennaro. "LHC: The First Band on the Web" (http://musiclub.web.cern. ch/MusiClub/bands/cernettes/firstband. html).

CERN MusiClub. CERN. . Retrieved 2010-09-24.

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Large Hadron Collider 22

External links

• Official website (http://lhc.web. cern.ch/lhc/)

• Overview of the LHC at CERN's public webpage (http://public. web. cern. ch/public/en/LHC/LHC-en.  html)

• CERN Courier magazine (http://www. cerncourier.com)

• CERN (http://twitter. com/cern) on Twitter

• CMS Experiment at CERN (http://twitter.com/CMSExperiment) on Twitter• Unofficial CERN (http://twitter.com/LHCExperiment) on Twitter

• LHC Portal (http://www.lhcportal. com/) Web portal

• Lyndon Evans and Philip Bryant (eds) (2008). "LHC Machine" (http://www. iop. org/EJ/journal/-page=extra.

lhc/jinst). Journal of Instrumentation 3: S08001. doi:10.1088/1748-0221/3/08/S08001. Full documentation for

design and construction of the LHC and its six detectors (1600p).

• symmetry magazine LHC special issue August 2006 (http://www. symmetrymagazine. org/cms/?pid=1000350),

special issue December 2007 (http://www.symmetrymagazine.org/cms/?pid=1000562)

• New Yorker: Crash Course (http://www. newyorker. com/reporting/2007/05/14/070514fa_fact_kolbert). The

world's largest particle accelerator.

• NYTimes: A Giant Takes On Physics' Biggest Questions (http://www. nytimes. com/2007/05/15/science/ 15cern. html?ex=1336881600&en=7825f6702d7071e7&ei=5090&partner=rssuserland&emc=rss).

• Why a Large Hadron Collider? (http://seedmagazine.com/news/2006/07/why_a_large_hadron_collider.php)

Seed Magazine interviews with physicists.

• Thirty collected pictures during commissioning and post- 19 September 2008 incident repair (http://www.

boston. com/bigpicture/2009/11/large_hadron_collider_ready_to.  html), from Boston Globe.

• Podcast Interview (http://omegataupodcast. net/2010/03/30-the-large-hadron-collider/) with CERN's Rolf 

Landua about the LHC and the physics behind it

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23

Experiments

List of LHC experimentsThis is a list of current and proposed experiments that take place, or would take place, at the CERN Large Hadron

Collider (LHC). The LHC is the most energetic particle collider in the world, and will be used to test the accuracy of 

the Standard Model (and particularly to search for the Higgs boson), and look for physics beyond the Standard

Model such as supersymmetry, extra dimensions, and others.

The list is first compiled from the SPIRES database, then missing information is retrieved from the online version

CERN's Grey Book . The most specific information of the two is kept, e.g. if the SPIRES database lists December

2008, while the Grey Book lists 22 December 2008, the Grey Book entry is shown. When there is a conflict between

the SPIRES database and the Grey Book , the SPIRES database information is listed, unless otherwise noted.

Large Hadron Collider experiments

LHC experiments

Experiment Location Spokesperson Description Proposed Approved Began Completed Link Website

ALICE IP2 Hans H.Gutbrod,

Eugenio Nappi,Jurgen Schukraft

 A l arge ion collider 

e xperiment : producingquark –gluon plasmaby colliding leadnuclei (~2.76 TeV)

?? 6 Feb1997

30March2010

N/A SPIRES[1]

Grey Book[2]

Website[3]

ATLAS IP1 FabiolaGianotti

[4] A  toroidal L HC 

 a pparatu s: sheddinglight on theinconsistencies of theStandard Model

Dec 1994 31 Jan1996

30March2010

N/A SPIRES[5]

Grey Book[6]

Website[7]

CMS IP5 Michel JeanDella Negra

C ompact  muon

 solenoid : samepurpose as for ATLAS

Oct 1992 31 Jan1996

30March2010

N/A SPIRES[8]

Grey Book[9]

Website[10]

LHCb IP8 Tatsuya Nakada  LHC   beautyexperiment : measuringcertain B-hadronqualities such asasymmetries and CPviolations,

?? 17 Sep1998

30March2010

N/A SPIRES[11]

Grey Book[12]

Website[13]

LHCf IP1 Yasushi Muraki LHC - f oward :measurement of neutral 0π mesonproduction, in order tounderstand ultra highenergy cosmic rays

?? 12 May2004

Notyet

N/A Grey Book[14]

Website[15]

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List of LHC experiments 24

FELIX IP4 Karsten Eggert,Cyrus Taylor

Forward elastic and

inelastic experiment atthe LHC

?? ?? ?? ?? SPIRES[16]

Website[17]

FP420 IP1, IP5 Brian Cox Foward protondetectors at 420 m

[from the ATLAS

and/or CMSinteraction point(s)]

?? ?? ?? ?? SPIRES[18]

Website[19]

HV-QF IP5 AntonioFerrando

Hadron very forwardcalorimeter, quartz

f iber option

?? ?? ?? ?? SPIRES[20]

Website[21]

MOEDAL IP8 James L. Pinfold Monopole and exoticparticle detector at the

LHC

July2009

[22]2

December2009

[23]

?? ?? SPIRES[24]

Website[25]

TOTEM IP5 Karsten Eggert Total cross section,elastic scattering anddiffraction

dissociation at theLHC

1999 18 May1999

Notyet

N/A SPIRES[26]

Grey Book[27]

Website[28]

See also

Experiments

• List of Super Proton Synchrotron experiments

Facilities

• CERN: European Organization for Nuclear Research

• PS: Proton Synchrotron• SPS: Super Proton Synchrotron

• ISOLDE: On-Line Isotope Mass Separator

• ISR: Intersecting Storage Rings

• LEP: Large Electron –Positron Collider

• LHC: Large Hadron Collider

Notes

[1] http://www. slac. stanford. edu/spires/find/experiments/www2?ee=CERN-LHC-ALICE

[2] http://greybook. cern. ch/programmes/experiments/ALICE. html

[3] http://aliceinfo. cern. ch/Collaboration/index.html[4] Previously Peter Jenni

[5] http://www. slac. stanford. edu/spires/find/experiments/www2?ee=CERN-LHC-ATLAS

[6] http://greybook. cern. ch/programmes/experiments/ATLAS. html

[7] http://atlas. web. cern. ch/Atlas/index.html

[8] http://www. slac. stanford. edu/spires/find/experiments/www2?ee=CERN-LHC-CMS

[9] http://greybook. cern. ch/programmes/experiments/CMS.html

[10] http://cms. cern. ch/iCMS/ 

[11] http://www. slac. stanford. edu/spires/find/experiments/www2?ee=CERN-LHC-B

[12] http://greybook.  cern. ch/programmes/experiments/LHCB. html

[13] http://lhcb. web. cern. ch/lhcb/ 

[14] http://greybook.  cern. ch/programmes/experiments/LHCF. html

[15] http://www. 

stelab. 

nagoya-u. 

ac.jp/LHCf/ [16] http://www. slac. stanford. edu/spires/find/experiments/www2?ee=CERN-LHC-FELIX

[17] http://felix. web. cern. ch/FELIX/ 

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List of LHC experiments 25

[18] http://www. slac. stanford. edu/spires/find/experiments/www2?ee=CERN-LHC-FP420

[19] http://www. fp420.  com/ 

[20] http://www. slac. stanford. edu/spires/find/experiments/www2?ee=CERN-LHC-HV-QF

[21] http://budoe. bu. edu/~sullivan/ 

[22] James Pinfold (2010). "The MoEDAL TDR" (http://web. me. com/jamespinfold/MoEDAL_site/TDR. html). . Retrieved 2010-04-11.

[23] James Pinfold (2010). "CERN Research Board Approves the MoEDAL Experiment" (http://web.  me. com/jamespinfold/MoEDAL_site/ 

MoEDAL_Milestones/Entries/2009/12/2_CERN_Research_Board_Approves_the_MoEDAL_Experiment. html). The MoEDAL Milestone

 Blog. . Retrieved 2010-04-11.[24] http://www. slac. stanford. edu/spires/find/experiments/www2?ee=CERN-LHC-MOEDAL

[25] http://web. me. com/jamespinfold/MoEDAL_site/Welcome.html

[26] http://www. slac. stanford. edu/spires/find/experiments/www2?ee=CERN-LHC-TOTEM

[27] http://greybook.  cern. ch/programmes/experiments/TOTEM. html

[28] http://totem. web. cern. ch/Totem/ 

References

• SPIRES team (http://www.slac. stanford. edu/spires/about/people.  shtml). "SPIRES database" (http://www.

slac. stanford. edu/spires/hep/). Stanford Linear Accelerator Center. Retrieved 2009-09-15.

• GS-AIF-FPF (http://ais. web. cern. ch/ais/manpower/). "Grey Book" (http://greybook.  cern. ch/). CERN.

Retrieved 2009-09-15.

External links

• CERN website (http://public. web. cern. ch/public/)

• LHC website (http://lhc. web.cern. ch/lhc/)

• CERN Grey Book (http://greybook.cern. ch/)

• SPIRES database (http://www. slac. stanford. edu/spires/)

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ALICE 26

ALICE

LHC experiments

ATLAS A Toroidal LHC Apparatus

CMS Compact Muon Solenoid

LHCb LHC-beauty

ALICE A Large Ion Collider Experiment

TOTEM Total Cross Section, Elastic Scattering and Diffraction Dissociation

LHCf  LHC-forward

MoEDAL Monopole and Exotics Detector At the LHC

LHC preaccelerators

p and Pb Linear accelerators for protons (Linac 2) and Lead (Linac 3)

(not marked) Proton Synchrotron Booster

PS Proton Synchrotron

SPS Super Proton Synchrotron

ALICE (A Large Ion Collider Experiment) is one of the six detector experiments being constructed at the Large

Hadron Collider at CERN. The other five are: ATLAS, CMS, TOTEM, LHCb, and LHCf. ALICE is optimized to

study heavy ion collisions. Pb-Pb nuclei collisions will be studied at a centre of mass energy of 2.76 TeV per

nucleon. The resulting temperature and energy density are expected to be large enough to generate a quark-gluon

plasma, a state of matter wherein quarks and gluons are deconfined.

Inner Tracking System

The Inner Tracking System (ITS) consists of six cylindrical layers of silicon detectors. The layers surround the

collision point and measure the properties of the emerging particles, pin-pointing their positions to a fraction of a

millimetre. The ITS will recognize particles containing heavy quarks by identifying the points at which they decay.

ITS layers (counting from the interaction point):

• 2 layers of SPD (Silicon Pixel Detector),

• 2 layers of SDD (Silicon Drift Detector),

• 2 layers of SSD (Silicon Strip Detector).

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ALICE 27

Time Projection Chamber

The ALICE Time Projection Chamber (TPC) is the main particle tracking device in ALICE. Charged particles

crossing the gas of the TPC ionize the gas atoms along their path, liberating electrons that drift towards the end

plates of the detector. An avalanche effect in the vicinity of the anode wires strung in the readout, will give the

necessary signal amplification. The positive ions created in the avalanche will induce a positive current signal on the

pad plane. The readout is done by the 557 568 pads that form the cathode plane of the multi-wire proportionalchambers (MWPC) located at the end plates. This gives the r and coordinates. The last coordinate, z, is given by

the drift time.

Transition Radiation Detector

The completed ALICE detector showing the

eighteen TRD modules (trapezoidal prisms in a

radial arrangement).

Electrons and positrons can be discriminated from other charged

particles using the emission of transition radiation, X-rays emitted

when the particles cross many layers of thin materials. To develop such

a Transition Radiation Detector (TRD) for ALICE many detector

prototypes were tested in mixed beams of pions and electrons.

Time of Flight

Charged particles are identified in ALICE by Time-Of-Flight (TOF);

heavier particles are slower and so take longer to reach the outer layers

of the detector. For its TOF system ALICE uses detectors called

Multigap Resistive Plate Chambers (MRPC). There are approximately

160 000 MRPC pads with time resolution of about 100 ps distributed

over the large surface of 150 square meters. Using the tracking information from other detectors every track firing a

sensor is identified.

Photon Spectrometer

The Photon Spectrometer (PHOS) is designed to measure the temperature of collisions by detecting photons

emerging from them. It will be made of lead tungstate crystals. When high energy photons strike lead tungstate, they

make it glow, or scintillate, and this glow can be measured. Lead tungstate is extremely dense (denser than iron),

stopping most photons that reach it.

High Momentum Particle Identification Detector

The High Momentum Particle Identification Detector (HMPID) is a RICH detector to determine the speed of particles beyond the momentum range available through energy loss (in ITS and TPC,  p = 600 MeV) and through

time-of-flight measurements (in TOF,  p = 1.2 –1.4 GeV). Its momentum range is up to 3 GeV for pion/kaon

discrimination and up to 5 GeV for kaon/proton discrimination. It is the world's largest caesium iodide RICH

detector, with an active area of 11 m². A prototype was successfully tested at CERN in 1997 and currently takes data

at the Relativistic Heavy Ion Collider at the Brookhaven National Laboratory in the US.

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ALICE 28

Muon spectrometer

The muon spectrometer measures pairs of muons, in particular those coming from the decays of J/ψ and Upsilon

particles. Tracking chambers to detect the muons and reconstruct their trajectories will be made from a special

composite material, which is highly rigid but very thin. A set of resistive plate chambers (RPC) will act as a

triggering device.

Forward Multiplicity Detectors

The Forward Multiplicity Detector (FMD) consist of 5 large silicon discs with each 10  240 individual detector

channels to measure the charged particles emitted at small angles relative to the beam. The forward detectors also

comprise the main trigger detectors for timing (T0) and for collision centrality (V0). Another important forward

detector in ALICE is the Photon Multiplicity Detector (PMD). This is a pre-shower detector which measures the

multiplicity and spatial distribution of photons produced in the collisions.

Electro-Magnetic Calorimeter

The Electro-Magnetic Calorimeter (EM-Cal) will add greatly to the high momentum particle measurementcapabilities of ALICE.

External links

• Official ALICE Public Webpage [1] at CERN

• ALICE section on US/LHC Website [2]

• ALICE photography panorama [3]

• Photography panorama of ALICE detector center [4]

• K. Aamodt et al. (ALICE collaboration) (2008). "The ALICE experiment at the CERN LHC" [5]. Journal of 

 Instrumentation 3 (8): S08002. doi:10.1088/1748-0221/3/08/S08002. (Full design documentation)

References

[1] http://aliceinfo. cern. ch/Public/Welcome. html

[2] http://www. uslhc. us/What_is_the_LHC/Experiments/ALICE

[3] http://petermccready. com/portfolio/07041606.html

[4] http://petermccready. com/portfolio/07041607.html

[5] http://www. iop. org/EJ/journal/-page=extra. lhc/jinst

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ATLAS 29

ATLAS

LHC experiments

ATLAS A Toroidal LHC Apparatus

CMS Compact Muon Solenoid

LHCb LHC-beauty

ALICE A Large Ion Collider Experiment

TOTEM Total Cross Section, Elastic Scattering and Diffraction Dissociation

LHCf  LHC-forward

MoEDAL Monopole and Exotics Detector At the LHC

LHC preaccelerators

p and Pb Linear accelerators for protons (Linac 2) and Lead (Linac 3)

(not marked) Proton Synchrotron Booster

PS Proton Synchrotron

SPS Super Proton Synchrotron

Geographical coordinates: 46°14′8″N 6°3′19″E

ATLAS logo.

ATLAS (A  Toroidal LHC ApparatuS) is one of the six particle detector

experiments (ALICE, ATLAS, CMS, TOTEM, LHCb, and LHCf) constructed at

the Large Hadron Collider (LHC), a new particle accelerator at the European

Organization for Nuclear Research (CERN) in Switzerland. ATLAS is 44 metres

long and 25 metres in diameter, weighing about 7,000 tonnes. The project is led by

Fabiola Gianotti and involves roughly 2,000 scientists and engineers at 165

institutions in 35 countries.[1] The construction was originally scheduled to be

completed in June 2007, but was ready and detected its first beam events on 10September 2008.[2] The experiment is designed to observe phenomena that involve

highly massive particles which were not observable using earlier lower-energy

accelerators and might shed light on new theories of particle physics beyond the

Standard Model.

The   ATLAS collaboration, the group of physicists building the detector, was

formed in 1992 when the proposed EAGLE (Experiment for Accurate Gamma,

Lepton and Energy Measurements) and ASCOT (Apparatus with Super

COnducting Toroids) collaborations merged their efforts into building a single, general-purpose particle detector for

the Large Hadron Collider.[3] The design was a combination of those two previous designs, as well as the detectorresearch and development that had been done for the Superconducting Supercollider. The ATLAS experiment was

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ATLAS 30

proposed in its current form in 1994, and officially funded by the CERN member countries beginning in 1995.

Additional countries, universities, and laboratories joined in subsequent years, and further institutions and physicists

continue to join the collaboration even today. The work of construction began at individual institutions, with detector

components shipped to CERN and assembled in the ATLAS experimental pit beginning in 2003.

ATLAS is designed as a general-purpose detector. When the proton beams produced by the Large Hadron Collider

interact in the center of the detector, a variety of different particles with a broad range of energies may be produced.Rather than focusing on a particular physical process, ATLAS is designed to measure the broadest possible range of 

signals. This is intended to ensure that, whatever form any new physical processes or particles might take, ATLAS

will be able to detect them and measure their properties. Experiments at earlier colliders, such as the Tevatron and

Large Electron-Positron Collider, were designed based on a similar philosophy. However, the unique challenges of 

the Large Hadron Collider —its unprecedented energy and extremely high rate of collisions —require ATLAS to be

larger and more complex than any detector ever built.

Background

ATLAS experiment detector under construction

in October 2004 in its experimental pit; the

current status of construction can be seen on theCERN website.

[4]Note the people in the

background, for comparison.

The first cyclotron, an early type of particle accelerator, was built by

Ernest O. Lawrence in 1931, with a radius of just a few centimetres

and a particle energy of 1 megaelectronvolt (MeV). Since then,

accelerators have grown enormously in the quest to produce new

particles of greater and greater mass. As accelerators have grown, so

too has the list of known particles that they might be used to

investigate. The most comprehensive model of particle interactions

available today is known as the Standard Model of Particle Physics.

With the important exception of the Higgs boson, all of the particles

predicted by the model have been observed. While the standard model

predicts that quarks, electrons, and neutrinos should exist, it does notexplain why the masses of the particles are so very different. Due to

this violation of "naturalness" most particle physicists believe it is

possible that the Standard Model will break down at energies beyond

the current energy frontier of about one teraelectronvolt (TeV) (set at the Tevatron). If such

beyond-the-Standard-Model physics is observed it is hoped that a new model, which is identical to the Standard

Model at energies thus far probed, can be developed to describe particle physics at higher energies. Most of the

currently proposed theories predict new higher-mass particles, some of which are hoped to be light enough to be

observed by ATLAS. At 27 kilometres in circumference, the Large Hadron Collider (LHC) will collide two beams of 

protons together, each proton carrying about 7 TeV of energy — enough energy to produce particles with masses up

to roughly ten times more massive than any particles currently known  — assuming of course that such particlesexist. With an energy seven million times that of the first accelerator the LHC represents a "new generation" of 

particle accelerators.

Particles that are produced in accelerators must also be observed, and this is the task of particle detectors. While

interesting phenomena may occur when protons collide it is not enough to just produce them. Particle detectors must

be built to detect particles, their masses, momentum, energies, charges, and nuclear spins. In order to identify all

particles produced at the interaction point where the particle beams collide, particle detectors are usually designed

with a similarity to an onion. The layers are made up of detectors of different types, each of which is adept at

observing specific types of particles. The different features that particles leave in each layer of the detector allow for

effective particle identification and accurate measurements of energy and momentum. (The role of each layer in thedetector is discussed below.) As the energy of the particles produced by the accelerator increases, the detectors

attached to it must grow to effectively measure and stop higher-energy particles. ATLAS is the largest detector ever

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ATLAS 31

built at a particle collider as of 2008.[1]

Physics Program

A schematic, called a Feynman diagram, of twovirtual gluons from colliding LHC protons

interacting to produce a hypothetical Higgs

boson, a top quark, and an antitop quark. These in

turn decay into a specific combination of quarks

and leptons that is very unlikely to be duplicated

by other processes. Collecting sufficient evidence

of signals like this one may eventually allow

ATLAS collaboration members to discover the

Higgs boson.

ATLAS is intended to investigate many different types of physics that

might become detectable in the energetic collisions of the LHC. Some

of these are confirmations or improved measurements of the StandardModel, while many others are searches for new physical theories.

One of the most important goals of ATLAS is to investigate a missing

piece of the Standard Model, the Higgs boson.[5] The Higgs

mechanism, which includes the Higgs boson, is invoked to give masses

to elementary particles, giving rise to the differences between the weak

force and electromagnetism by giving the W and Z bosons masses

while leaving the photon massless. If the Higgs boson is not discovered

by ATLAS, it is expected that another mechanism of electroweak

symmetry breaking that explains the same phenomena, such astechnicolour, will be discovered. The Standard Model is simply not

mathematically consistent at the energies of the LHC without such a

mechanism. The Higgs boson would be detected by the particles it

decays into; the easiest to observe are two photons, two bottom quarks,

or four leptons. Sometimes these decays can only be definitively

identified as originating with the Higgs boson when they are associated

with additional particles; for an example of this, see the diagram at

right.

The asymmetry between the behavior of matter and antimatter, known as CP violation, will also be investigated.[5]

Current CP-violation experiments, such as BaBar and Belle, have not yet detected sufficient CP violation in the

Standard Model to explain the lack of detectable antimatter in the universe. It is possible that new models of physics

will introduce additional CP violation, shedding light on this problem; these models might either be detected directly

by the production of new particles, or indirectly by measurements made of the properties of B-mesons. (LHCb, an

LHC experiment dedicated to B-mesons, is likely to be better suited to the latter).[6]

The top quark, discovered at Fermilab in 1995, has thus far had its properties measured only approximately. With

much greater energy and greater collision rates, LHC will produce a tremendous number of top quarks, allowing

ATLAS to make much more precise measurements of its mass and interactions with other particles. [7] These

measurements will provide indirect information on the details of the Standard Model, perhaps revealing

inconsistencies that point to new physics. Similar precision measurements will be made of other known particles; forexample, ATLAS may eventually measure the mass of the W boson twice as accurately as has previously been

achieved.

Perhaps the most exciting lines of investigation are those searching directly for new models of physics. One theory

that is the subject of much current research is broken supersymmetry. The theory is popular because it could

potentially solve a number of problems in theoretical physics and is present in almost all models of string theory.

Models of supersymmetry involve new, highly massive particles; in many cases these decay into high-energy quarks

and stable heavy particles that are very unlikely to interact with ordinary matter. The stable particles would escape

the detector, leaving as a signal one or more high-energy quark jets and a large amount of "missing" momentum.

Other hypothetical massive particles, like those in Kaluza-Klein theory, might leave a similar signature, but its

discovery would certainly indicate that there was some kind of physics beyond the Standard Model.

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ATLAS 32

One remote possibility (if the universe contains large extra dimensions) is that microscopic black holes might be

produced by the LHC.[8] These would decay immediately by means of Hawking radiation, producing all particles in

the Standard Model in equal numbers and leaving an unequivocal signature in the ATLAS detector.[9] In fact, if this

occurs, the primary studies of Higgs bosons and top quarks would be conducted on those produced by the black

holes.

Components

The ATLAS detector consists of a series of ever-larger concentric cylinders around the interaction point where the

proton beams from the LHC collide. It can be divided into four major parts: the Inner Detector, the calorimeters, the

muon spectrometer and the magnet systems.[10] Each of these is in turn made of multiple layers. The detectors are

complementary: the Inner Detector tracks particles precisely, the calorimeters measure the energy of easily stopped

particles, and the muon system makes additional measurements of highly penetrating muons. The two magnet

systems bend charged particles in the Inner Detector and the muon spectrometer, allowing their momenta to be

measured.

The only established stable particles that cannot be detected directly are neutrinos; their presence is inferred by

noticing a momentum imbalance among detected particles. For this to work, the detector must be "hermetic", and

detect all non-neutrinos produced, with no blind spots. Maintaining detector performance in the high radiation areas

immediately surrounding the proton beams is a significant engineering challenge.

Inner detector

The ATLAS TRT central section, the outermost

part of the Inner Detector, as of September 2005,

assembled on the surface and taking data from

cosmic rays.

The Inner Detector begins a few centimetres from the proton beam

axis, extends to a radius of 1.2 metres, and is seven metres in length

along the beam pipe. Its basic function is to track charged particles by

detecting their interaction with material at discrete points, revealing

detailed information about the type of particle and its momentum.[11]

The magnetic field surrounding the entire inner detector causes

charged particles to curve; the direction of the curve reveals a particle's

charge and the degree of curvature reveals its momentum. The starting

points of the tracks yield useful information for identifying particles;

for example, if a group of tracks seem to originate from a point other

than the original proton –proton collision, this may be a sign that the

particles came from the decay of a bottom quark (see B-tagging). The

Inner Detector has three parts, which are explained below.

The Pixel Detector, the innermost part of the detector, contains three layers and three disks on each end-cap, with a

total of 1744 modules, each measuring two centimetres by six centimetres. The detecting material is 250 µm thick

silicon. Each module contains 16 readout chips and other electronic components. The smallest unit that can be read

out is a pixel (each 50 by 400 micrometres); there are roughly 47,000 pixels per module. The minute pixel size is

designed for extremely precise tracking very close to the interaction point. In total, the Pixel Detector will have over

80 million readout channels, which is about 50% of the total readout channels; such a large count created a design

and engineering challenge. Another challenge was the radiation the Pixel Detector will be exposed to because of its

proximity to the interaction point, requiring that all components be radiation hardened in order to continue operating

after significant exposures.

The Semi-Conductor Tracker (SCT) is the middle component of the inner detector. It is similar in concept and

function to the Pixel Detector but with long, narrow strips rather than small pixels, making coverage of a larger areapractical. Each strip measures 80 micrometres by 12.6 centimetres. The SCT is the most critical part of the inner

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ATLAS 33

detector for basic tracking in the plane perpendicular to the beam, since it measures particles over a much larger area

than the Pixel Detector, with more sampled points and roughly equal (albeit one dimensional) accuracy. It is

composed of four double layers of silicon strips, and has 6.2 million readout channels and a total area of 61 square

meters.

The Transition radiation tracker (TRT), the outermost component of the inner detector, is a combination of a straw

tracker and a transition radiation detector. The detecting elements are drift tubes (straws), each four millimetres indiameter and up to 144 centimetres long. The uncertainty of track position measurements (position resolution) is

about 200 micrometres, not as precise as those for the other two detectors, a necessary sacrifice for reducing the cost

of covering a larger volume and having transition radiation detection capability. Each straw is fil led with gas that

becomes ionized when a charged particle passes through. The straws are held at about -1500V, driving the negative

ions to a fine wire down the centre of each straw, producing a current pulse (signal) in the wire. The wires with

signals create a pattern of 'hit' straws that allow the path of the particle to be determined. Between the straws,

materials with widely varying indices of refraction cause ultra-relativistic charged particles to produce transition

radiation and leave much stronger signals in some straws. Xenon gas is used to increase the number of straws with

strong signals. Since the amount of transition radiation is greatest for highly relativistic particles (those with a speed

very near the speed of light), and particles of a particular energy have a higher speed the lighter they are, particlepaths with many very strong signals can be identified as the lightest charged particles, electrons. The TRT has about

298,000 straws in total.

Calorimeters

September 2005: the main barrel section of the

ATLAS hadronic calorimeter, waiting to be

moved inside the toroid magnets.

One of the sections of the extensions of the

hadronic calorimeter, waiting to be inserted in

late February 2006

The calorimeters are situated outside the solenoidal magnet that

surrounds the inner detector. Their purpose is to measure the energy

from particles by absorbing it. There are two basic calorimeter

systems: an inner electromagnetic calorimeter and an outer hadronic

calorimeter.[12] Both are sampling calorimeters; that is, they absorb

energy in high-density metal and periodically sample the shape of the

resulting particle shower, inferring the energy of the original particle

from this measurement.

The electromagnetic (EM) calorimeter absorbs energy from particles

that interact electromagnetically, which include charged particles and

photons. It has high precision, both in the amount of energy absorbed

and in the precise location of the energy deposited. The angle between

the particle's trajectory and the detector's beam axis (or more precisely

the pseudorapidity) and its angle within the perpendicular plane are

both measured to within roughly 0.025 radians. The energy-absorbingmaterials are lead and stainless steel, with liquid argon as the sampling

material, and a cryostat is required around the EM calorimeter to keep

it sufficiently cool.

The hadron calorimeter absorbs energy from particles that pass through

the EM calorimeter, but do interact via the strong force; these particles

are primarily hadrons. It is less precise, both in energy magnitude and

in the localization (within about 0.1 radians only).[6] The

energy-absorbing material is steel, with scintillating tiles that sample

the energy deposited. Many of the features of the calorimeter are chosen for their cost-effectiveness; the instrument

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ATLAS 34

is large and comprises a huge amount of construction material: the main part of the calorimeter —the tile

calorimeter —is eight metres in diameter and covers 12 metres along the beam axis. The far-forward sections of the

hadronic calorimeter are contained within the EM calorimeter's cryostat, and use liquid argon as it does.

Muon spectrometer

The muon spectrometer is an extremely large tracking system, extending from a radius of 4.25 m around thecalorimeters out to the full radius of the detector (11 m).[10] Its tremendous size is required to accurately measure the

momentum of muons, which penetrate other elements of the detector; the effort is vital because one or more muons

are a key element of a number of interesting physical processes, and because the total energy of particles in an event

could not be measured accurately if they were ignored. It functions similarly to the inner detector, with muons

curving so that their momentum can be measured, albeit with a different magnetic field configuration, lower spatial

precision, and a much larger volume. It also serves the function of simply identifying muons —very few particles of 

other types are expected to pass through the calorimeters and subsequently leave signals in the muon spectrometer. It

has roughly one million readout channels, and its layers of detectors have a total area of 12,000 square meters.

Magnet system

The ends of four of eight ATLAS toroid magnets,seen from the surface, about 90 metres above, in

September 2005.

The ATLAS detector uses two large superconducting magnet systems

to bend charged particles so that their momenta can be measured. This

bending is due to the Lorentz force, which is proportional to velocity.

Since all particles produced in the LHC's proton collisions will be

traveling at very close to the speed of light, the force on particles of 

different momenta is equal. (In the theory of relativity, momentum is

not  proportional to velocity at such speeds.) Thus high-momentum

particles will curve very little, while low-momentum particles will

curve significantly; the amount of curvature can be quantified and the

particle momentum can be determined from this value.

The inner solenoid produces a two tesla magnetic field surrounding the

Inner Detector.[13] This high magnetic field allows even very energetic

particles to curve enough for their momentum to be determined, and its nearly uniform direction and strength allow

measurements to be made very precisely. Particles with momenta below roughly 400 MeV will be curved so strongly

that they will loop repeatedly in the field and most likely not be measured; however, this energy is very small

compared to the several TeV of energy released in each proton collision.

The outer toroidal magnetic field is produced by eight very large air-core superconducting barrel loops and two

end-caps, all situated outside the calorimeters and within the muon system.[13] This magnetic field is 26 metres long

and 20 metres in diameter, and it stores 1.6 gigajoules of energy. Its magnetic field is not uniform, because a

solenoid magnet of sufficient size would be prohibitively expensive to build. Fortunately, measurements need to be

much less precise to measure momentum accurately in the large volume of the muon system.

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ATLAS 35

Part of the ATLAS, as it looked February 2007.

Forward detectors

The ATLAS detector will be complemented with a set of detectors in

the very forward region. These detectors will be located in the LHC

tunnel far away from the interaction point. The basic idea is to measure

elastic scattering at very small angles in order to get a handle on theabsolute luminosity at the interaction point of ATLAS.

Data systems and analysis

The detector generates unmanageably large amounts of raw data, about 25 megabytes per event (raw; zero

suppression reduces this to 1.6 MB) times 40 million beam crossings per second in the center of the detector, for a

total of 1 petabyte/second of raw data.[14] The trigger system uses simple information to identify, in real time, the

most interesting events to retain for detailed analysis. There are three trigger levels, the first based in electronics on

the detector and the other two primarily run on a large computer cluster near the detector. After the first-level trigger,

about 100,000 events per second have been selected. After the third-level trigger, a few hundred events remain to be

stored for further analysis. This amount of data will require over 100 megabytes of disk space per second  — at least

a petabyte each year.[15]

Offline event reconstruction will be performed on all permanently stored events, turning the pattern of signals fromthe detector into physics objects, such as jets, photons, and leptons. Grid computing will be extensively used for

event reconstruction, allowing the parallel use of university and laboratory computer networks throughout the world

for the CPU-intensive task of reducing large quantities of raw data into a form suitable for physics analysis. The

software for these tasks has been under development for many years, and will continue to be refined once the

experiment is running.

Individuals and groups within the collaboration will write their own code to perform further analysis of these objects,

searching in the pattern of detected particles for particular physical models or hypothetical particles. These studies

are already being developed and tested on detailed simulations of particles and their interactions with the detector.

Such simulations give physicists a good sense of which new particles can be detected and how long it will take to

confirm them with sufficient statistical certainty.

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ATLAS 36

Notes

[1] CERN (2006-11-20). "World's largest superconducting magnet switches on" (http://press. web. cern. ch/Press/PressReleases/ 

Releases2006/PR17. 06E. html). Press release. . Retrieved 2007-03-03.

[2] "First beam and first events in ATLAS" (http://www. atlas.ch/news/2008/first-beam-and-event. html). Atlas.ch. . Retrieved 2008-09-13.

[3] "ATLAS Collaboration records" (http://library. cern.ch/archives/isad/isaatlas.html). CERN Archive. . Retrieved 2007-02-25.

[4] "UX15 Installation; WEB cameras" (http://atlaseye-webpub.web. cern. ch/atlaseye-webpub/web-sites/pages/UX15_webcams. htm).

 ATLAS Control Room. cern.ch. . Retrieved September 15, 2010.[5] "Introduction and Overview" (http://atlas. web. cern.ch/Atlas/TP/NEW/HTML/tp9new/node4.

html#SECTION00400000000000000000).  ATLAS Technical Proposal. CERN. 1994. .

[6] N. V. Krasnikov, V. A. Matveev (September 1997). "Physics at LHC" (http://arxiv.  org/abs/hep-ph/9703204). Physics of Particles and 

 Nuclei 28 (5): 441 –470. doi:10.1134/1.953049. .

[7] "Top-Quark Physics" (http://atlas. web.cern. ch/Atlas/TP/NEW/HTML/tp9new/node416. html#SECTION0024100000000000000000).

 ATLAS Technical Proposal. CERN. 1994. .

[8] C.M. Harris, M.J. Palmer, M.A. Parker, P. Richardson, A. Sabetfakhri and B.R. Webber (2005). "Exploring higher dimensional black holes at

the Large Hadron Collider". Journal of High Energy Physics  5: 053. doi:10.1088/1126-6708/2005/05/053.

[9] J. Tanaka, T. Yamamura, S. Asai, J. Kanzaki (2005). "Study of Black Holes with the ATLAS detector at the LHC" (http://www.

springerlink. com/content/x067g845688470r4/).The European Physical Journal C  41 (s2): 19 –33. doi:10.1140/epjcd/s2005-02-008-x. .

[10] "Overall detector concept" (http://atlas.web. cern. ch/Atlas/TP/NEW/HTML/tp9new/node6. html#SECTION00420000000000000000).

 ATLAS Technical Proposal. CERN. 1994. .

[11] "Inner detector" (http://atlas. web. cern.ch/Atlas/TP/NEW/HTML/tp9new/node10.  html#SECTION00433000000000000000).  ATLAS 

Technical Proposal. CERN. 1994. .

[12] "Calorimetry" (http://atlas. web. cern.ch/Atlas/TP/NEW/HTML/tp9new/node9.  html#SECTION00432000000000000000).  ATLAS 

Technical Proposal. CERN. 1994. .

[13] "Magnet system" (http://atlas. web. cern.ch/Atlas/TP/NEW/HTML/tp9new/node8.  html#SECTION00431000000000000000).  ATLAS 

Technical Proposal. CERN. 1994. .

[14] Marjorie Shapiro. (June 18, 2007). Supersymmetry, Extra Dimensions and the Origin of Mass: Exploring the Nature of the Universe Using

 PetaScale Data Analysis (http://www.youtube.com/watch?v=-cdbnwaW34g). Event occurs at 35:00. . Retrieved 2007-12-08. See also

32:30 for information on the various trigger levels.

[15] "The sensitive giant" (http://www.eurekalert. org/features/doe/2004-03/dnal-tsg032604. php). United States Department of Energy

 Research News. March 2004. .

References

• ATLAS Technical Proposal. (http://atlas.web. cern.ch/Atlas/TP/tp.  html) CERN: The Atlas Experiment.

Retrieved on 2007-04-10

• ATLAS Detector and Physics Performance Technical Design Report. (http://atlas. web. cern. ch/Atlas/ 

GROUPS/PHYSICS/TDR/access.html) CERN: The Atlas Experiment. Retrieved on 2007-04-10

• N. V. Krasnikov, V. A. Matveev (September 1997). "Physics at LHC" (http://arxiv. org/abs/hep-ph/9703204).

 Physics of Particles and Nuclei 28 (5): 441 –470. doi:10.1134/1.953049.

External links

• Official ATLAS Public Webpage (http://atlas. ch) at CERN (The "award winning ATLAS movie" is a very good 

general introduction!)

• Official ATLAS Collaboration Webpage (http://atlas. web.cern.ch/Atlas/internal/Welcome.  html) at CERN

(Lots of technical and logistical information)

• ATLAS Cavern Webcams (http://atlaseye-webpub. web.cern. ch/atlaseye-webpub/web-sites/pages/ 

UX15_webcams. htm)

• Time lapse video of the assembly (http://www. youtube. com/watch?v=kVrUR_SOykk)

• ATLAS section from US/LHC Website (http://www. uslhc.us/What_is_the_LHC/Experiments/ATLAS)

• PhysicsWorld article on LHC and experiments (http://physicsweb. org/articles/world/13/5/9/1)

• New York Times article on LHC and experiments (http://www. 

nytimes.com/2000/11/21/science/21HIGG.html?ex=1130040000&en=5282f51cf019f1b7&ei=5070&ex=1082001600&en=39ccf65ca6047eb2&ei=5070)

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ATLAS 37

• United States Department of Energy article on ATLAS (http://www. eurekalert. org/features/doe/2004-03/ 

dnal-tsg032604. php)

• The Large Hadron Collider ATLAS Experiment Virtual Reality (VR) photography panoramas (http://www.

petermccready. com/portfolio/05091901.  html)

• Large Hadron Collider Project Director Dr Lyn Evans CBE on the engineering behind the ATLAS experiment,

 Ingenia magazine, June 2008 (http://www.ingenia.org.  uk/ingenia/articles.  aspx?Index=489)

• Atlas Experiment News and social networking (http://www.AtlasExperiment. net)

• The ATLAS Collaboration, G Aad et al. (2008-08-14). "The ATLAS Experiment at the CERN Large Hadron

Collider" (http://www. iop. org/EJ/journal/-page=extra.  lhc/jinst). Journal of Instrumentation 3 (S08003):

S08003. doi:10.1088/1748-0221/3/08/S08003. Retrieved 2008-08-26. (Full design documentation)

• Press release from October 2008 by EB Industries regarding the ATLAS project (http://ebindustries. com/ 

ATLAS article. pdf)

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CMS 38

CMS

Geographical coordinates: 46°18′34″N 6°4′37″E

LHC experiments

ATLAS A Toroidal LHC Apparatus

CMS Compact Muon Solenoid

LHCb LHC-beauty

ALICE A Large Ion Collider Experiment

TOTEM Total Cross Section, Elastic Scattering and Diffraction Dissociation

LHCf  LHC-forward

MoEDAL Monopole and Exotics Detector At the LHC

LHC preaccelerators

p and Pb Linear accelerators for protons (Linac 2) and Lead (Linac 3)

(not marked) Proton Synchrotron Booster

PS Proton SynchrotronSPS Super Proton Synchrotron

View of the CMS endcap through the barrel sections. The ladder to the lower right

gives an impression of scale.

The Compact Muon Solenoid (CMS)

experiment is one of two large

general-purpose particle physics detectors

built on the proton-proton Large Hadron

Collider (LHC) at CERN in Switzerland and

France. Approximately 3,600 people from

183 scientific institutes, representing 38

countries form the CMS collaboration whobuilt and now operate the detector.[1] It is

located in an underground cavern at Cessy

in France, just across the border from

Geneva.

Background

Recent collider experiments such as the now-dismantled Large Electron-Positron Collider at CERN and the (as of 

2010) still running Tevatron at Fermilab have provided remarkable insights into, and precision tests of the Standard

Model of Particle Physics. However, a number of questions remain unanswered.

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CMS 39

A principal concern is the lack of any direct evidence for the Higgs Boson, the particle resulting from the Higgs

mechanism which provides an explanation for the masses of elementary particles. Other questions include

uncertainties in the mathematical behaviour of the Standard Model at high energies, the lack of any particle physics

explanation for dark matter and the reasons for the imbalance of matter and antimatter observed in the Universe.

The Large Hadron Collider and the associated experiments are designed to address a number of these questions.

Physics goals

The main goals of the experiment are:

• to explore physics at the TeV scale

• to discover the Higgs boson

• to look for evidence of physics beyond the standard model, such as supersymmetry, or extra dimensions

• to study aspects of heavy ion collisions

The ATLAS experiment, at the other side of the LHC ring is designed with similar goals in mind, and the two

experiments are designed to complement each other both to extend reach and to provide corroboration of findings.

Detector summary

CMS is designed as a general-purpose detector, capable of studying many aspects of proton collisions at 14 TeV, the

center-of-mass energy of the LHC particle accelerator. It contains subsystems which are designed to measure the

energy and momentum of photons, electrons, muons, and other products of the collisions. The innermost layer is a

silicon-based tracker. Surrounding it is a scintillating crystal electromagnetic calorimeter, which is itself surrounded

with a sampling calorimeter for hadrons. The tracker and the calorimetry are compact enough to fit inside the CMS

solenoid which generates a powerful magnetic field of 3.8 T. Outside the magnet are the large muon detectors, which

are inside the return yoke of the magnet.

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CMS 40

CMS by layers

For full technical details about the CMS detector, please see the Technical Design Report [2].

The interaction point

This is the point in the centre of the detector at which proton-proton collisions occur between the two

counter-rotating beams of the LHC. At each end of the detector magnets focus the beams into the interaction point.

At collision each beam has a radius of 17 μm and the crossing angle between the beams is 285 μrad.

At full design luminosity each of the two LHC beams will contain 2,808 bunches of 1.15 × 1011 protons. The

interval between crossings is 25 ns, although the number of collisions per second is only 31.6 million due to gaps in

the beam as injector magnets are activated and deactivated.

At full luminosity each collision will produce an average of 20 proton-proton interactions. The collisions occur at a

centre of mass energy of 14 TeV. It is worth noting that the actual interactions occur between quarks rather than

protons, and so the actual energy involved in each collision will be lower, as determined by the parton distributionfunctions.

The first which ran in September 2008 was expected to operate at a lower collision energy of 10 TeV but this was

prevented by the 19 September 2008 shutdown. When at this target level, the LHC will have a significantly reduced

luminosity, due to both fewer proton bunches in each beam and fewer protons per bunch. The reduced bunch

frequency does allow the crossing angle to be reduced to zero however, as bunches are far enough spaced to prevent

secondary collisions in the experimental beampipe.

Layer 1 – The tracker

The silicon strip tracker of CMS.

Immediately around the interaction point the inner tracker serves toidentify the tracks of individual particles and match them to the

vertices from which they originated. The curvature of charged particle

tracks in the magnetic field allows their charge and momentum to be

measured.

The CMS silicon tracker consists of 13 layers in the central region and

14 layers in the endcaps. The innermost three layers (up to 11 cm

radius) consist of 100×150 μm pixels, 66 million in total.

The next four layers (up to 55 cm radius) consist of 10 cm × 180 μm

silicon strips, followed by the remaining six layers of 25 cm × 180 μm

strips, out to a radius of 1.1 m. There are 9.6 million strip channels in total.

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CMS 41

During full luminosity collisions the occupancy of the pixel layers per event is expected to be 0.1%, and 1 –2% in the

strip layers. The expected SLHC upgrade will increase the number of interactions to the point where over-occupancy

may significantly reduce trackfinding effectiveness.

This part of the detector is the world's largest silicon detector. It has 205 m 2 of silicon sensors (approximately the

area of a tennis court) comprising 76 million channels.[3]

Layer 2 – The Electromagnetic Calorimeter

The Electromagnetic Calorimeter (ECAL) is designed to measure with high accuracy the energies of electrons and

photons.

The ECAL is constructed from crystals of lead tungstate, PbWO4. This is an extremely dense but optically clear

material, ideal for stopping high energy particles. It has a radiation length of χ0

= 0.89 cm, and has a rapid light

yield, with 80% of light yield within one crossing time (25 ns). This is balanced however by a relatively low light

yield of 30 photons per MeV of incident energy.

The crystals used have a front size of 22 mm × 22 mm and a depth of 230 mm. They are set in a matrix of carbon

fibre to keep them optically isolated, and backed by silicon avalanche photodiodes for readout. The barrel region

consists of 61,200 crystals, with a further 7,324 in each of the endcaps.

At the endcaps the ECAL inner surface is covered by the preshower subdetector, consisting of two layers of lead

interleaved with two layers of silicon strip detectors. Its purpose is to aid in pion-photon discrimination.

Preparing lead tungstate crystals for the ECAL

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CMS 42

Layer 3 – The Hadronic Calorimeter

Half of the Hadron Calorimeter

The purpose of the Hadronic Calorimeter (HCAL) is both to

measure the energy of individual hadrons produced in each event,

and to be as near to hermetic around the interaction region as

possible to allow events with missing energy to be identified.

The HCAL consists of layers of dense material (brass or steel)

interleaved with tiles of plastic scintillators, read out via

wavelength-shifting fibres by hybrid photodiodes. This

combination was determined to allow the maximum amount of 

absorbing material inside of the magnet coil.

The high pseudorapidity region is instrumented by the Hadronic Forward detector. Located

11 m either side of the interaction point, this uses a slightly different technology of steel absorbers and quartz fibresfor readout, designed to allow better separation of particles in the congested forward region.

The brass used in the endcaps of the HCAL used to be Russian artillery shells.[4]

Layer 4 – The magnet

Like most particle physics detectors, CMS has a large solenoid magnet. This allows the charge/mass ratio of particles

to be determined from the curved track that they follow in the magnetic field. It is 13 m long and 6 m in diameter,

and its refrigerated superconducting niobium-titanium coils were originally intended to produce a 4 T magnetic field.

It was recently announced that the magnet will run at 3.8 T instead of the full design strength in order to maximize

longevity.[5]

The inductance of the magnet is 14 Η and the nominal current for 4 T is 19,500 A, giving a total stored energy of 2.66 GJ, equivalent to about half-a-tonne of TNT. There are dump circuits to safely dissipate this energy should the

magnet quench. The circuit resistance (essentially just the cables from the power converter to the cryostat) has a

value of 0.1 mΩ which leads to a circuit time constant of nearly 39 hours. This is the longest time constant of any

circuit at CERN. The operating current for 3.8 T is 18,160 A, giving a stored energy of 2.3 GJ.

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CMS 43

Layer 5 – The muon detectors and return yoke

To identify muons and measure their momenta, CMS uses three types of detector: drift tubes (DT), cathode strip

chambers (CSC) and resistive plate chambers (RPC). The DTs are used for precise trajectory measurements in the

central barrel region, while the CSCs are used in the end caps. The RPCs provide a fast signal when a muon passes

through the muon detector, and are installed in both the barrel and the end caps.

The Hadron Calorimeter Barrel (in the foreground, on the yellow

frame) waits to be inserted into the superconducting magnet (the silver

cylinder in the centre of the red magnet yoke).

A part of the Magnet Yoke,

with drift tubes and

resistive-plate chambers in

the barrel region.

Collecting and collating the data

Pattern recognition

Testing the data read-out electronics for the tracker.

New particles discovered in CMS will be typically unstable andrapidly transform into a cascade of lighter, more stable and better

understood particles. Particles travelling through CMS leave

behind characteristic patterns, or ‘signatures’, in the different

layers, allowing them to be identified. The presence (or not) of any

new particles can then be inferred.

Trigger system

To have a good chance of producing a rare particle, such as a

Higgs boson, a very large number of collisions are required. Mostcollision events in the detector are "soft" and do not produce

interesting effects. The amount of raw data from each crossing is

approximately 1 MB, which at the 40 MHz crossing rate would

result in 40 TB of data a second, an amount that the experiment

cannot hope to store or even process properly. The trigger system

reduces the rate of interesting events down to a manageable 100

per second.

To accomplish this, a series of "trigger" stages are employed. All

the data from each crossing is held in buffers within the detector

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CMS 44

while a small amount of key information is used to perform a fast, approximate calculation to identify features of 

interest such as high energy jets, muons or missing energy. This "Level 1" calculation is completed in around 1 µs,

and event rate is reduced by a factor of about thousand down to 50 kHz. All these calculations are done on fast,

custom hardware using reprogrammable FPGAs.

If an event is passed by the Level 1 trigger all the data still buffered in the detector is sent over fibre-optic links to

the "High Level" trigger, which is software (mainly written in C++) running on ordinary computer servers. Thelower event rate in the High Level trigger allows time for much more detailed analysis of the event to be done than

in the Level 1 trigger. The High Level trigger reduces the event rate by a further factor of about a thousand down to

around 100 events per second. These are then stored on tape for future analysis.

Data analysis

Data that has passed the triggering stages and been stored on tape is duplicated using the Grid to additional sites

around the world for easier access and redundancy. Physicists are then able to use the Grid to access and run their

analyses on the data.

Some possible analyses might be:

• Looking at events with large amounts of apparently missing energy, which implies the presence of particles that

have passed through the detector without leaving a signature, such as neutrinos.

• Looking at the kinematics of pairs of particles produced by the decay of a parent, such as the Z boson decaying to

a pair of electrons or the Higgs boson decaying to a pair of tau leptons or photons, to determine the properties and

mass of the parent.

• Looking at jets of particles to study the way the quarks in the collided protons have interacted.

Milestones

1998 Construction of surface buildings for CMS begins.2000 LEP shut down, construction of cavern begins.

2004 Cavern completed.

10 September 2008 First beam in CMS.

23 November 2009 First collisions in CMS.

30 March 2010 First 7 TeV collisions in CMS.

The insertion of the vacuum tank,

June 2002

YE+2 descent into the cavern YE+1, a component of CMS

weighing 1,270 tonnes, finishes

its 100 m descent into the CMS

cavern, January 2007

Computer-generated event

display of protons hitting a

tungsten block just upstream

of CMS on the first beam

day, September 2008

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CMS 45

References

[1] (http://cms-project-cmsinfo. web. cern.ch/cms-project-cmsinfo/Collaboration/index. html)

[2] http://cdsweb. cern. ch/record/922757/files/lhcc-2006-001.pdf 

[3] CMS installs the world's largest silicon detector (http://cerncourier.  com/cws/article/cern/32915), CERN Courier, Feb 15, 2008

[4] CMS HCAL history - CERN (http://cms.web.cern. ch/cms/Detector/HCAL/History.  html)

[5] http://iopscience. iop. org/1748-0221/5/03/T03021/pdf/1748-0221_5_03_T03021. pdf Precise mapping of the magnetic field in the CMS

barrel yoke using cosmic rays

• Della Negra, Michel; Petrilli, Achille; Herve, Alain; Foa, Lorenzo; (2006) (PDF). CMS Physics Technical Design

 Report Volume I: Software and Detector Performance (http://doc.  cern. ch//archive/electronic/cern/preprints/ 

lhcc/public/lhcc-2006-001.  pdf). CERN.

External links

• CMS home page (http://cms. cern. ch/)

• CMS Outreach (http://cmsinfo.cern. ch/)

• CMS Times (http://cmsinfo. cern. ch/outreach/CMSTimes.html)

• CMS section from US/LHC Website (http://www.uslhc. 

us/What_is_the_LHC/Experiments/CMS)• http://petermccready. com/portfolio/07041601.  html (http://petermccready. com/portfolio/07041601.html)

Panoramic view - click and drag to look around the experiment under construction (with sound!) (requires

Quicktime)

• The assembly of the CMS detector, step by step, through a 3D animation (http://www. youtube. com/ 

watch?v=7FiLC2m4oR8)

• The CMS Collaboration, S Chatrchyan et al. (2008-08-14). "The CMS experiment at the CERN LHC" (http:// 

www. iop. org/EJ/journal/-page=extra.  lhc/jinst). Journal of Instrumentation 3: S08004.

doi:10.1088/1748-0221/3/08/S08004. Retrieved 2008-08-26 (Full design documentation)

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LHCb 46

LHCb

Geographical coordinates: 46°14′27.64″N 6°5′48.96″E

LHC experiments

ATLAS A Toroidal LHC Apparatus

CMS Compact Muon Solenoid

LHCb LHC-beauty

ALICE A Large Ion Collider Experiment

TOTEM Total Cross Section, Elastic Scattering and Diffraction Dissociation

LHCf  LHC-forward

MoEDAL Monopole and Exotics Detector At the LHC

LHC preaccelerators

p and Pb Linear accelerators for protons (Linac 2) and Lead (Linac 3)

(not marked) Proton Synchrotron Booster

PS Proton SynchrotronSPS Super Proton Synchrotron

The LHCb (standing for "Large Hadron Collider beauty" where "beauty" refers to the bottom quark) experiment is

one of six particle physics detector experiments built on the Large Hadron Collider accelerator at CERN. LHCb is a

specialized b-physics experiment, particularly aimed at measuring the parameters of CP violation in the interactions

of b-hadrons (heavy particles containing a bottom quark).

The LHCb detector

The fact that both B hadrons are predominantly produced in the same forward cone as B meson production is

exploited in the layout of the LHCb detector. The LHCb detector is a single arm forward spectrometer with a polar

angular coverage from 10 to 300 milliradians (mrad) in the horizontal and 250 mrad in the vertical plane. The

asymmetry between the horizontal and vertical plane is determined by a large dipole magnet with the main

component in the vertical direction.

The vertex detector (known as the vertex locator or VELO) is built around the proton interaction region. It is used to

measure the particle trajectories close to the interaction point in order to precisely separate primary and secondary

vertices, e.g. for B-tagging.

The RICH-1 detector (Ring imaging Cherenkov detector) is located directly after the vertex detector. It is used for

particle identification of low-momentum tracks.

The main tracking system is placed before and after the dipole magnet. It is used to reconstruct the trajectories of charged particles and to measure their momenta.

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LHCb 47

Following the tracking system is RICH-2. It allows the identification of the particle type of high-momentum tracks.

The electromagnetic and hadronic calorimeters provide measurement of the energy of electrons, photons, and

hadrons. These measurements are used at trigger level to identify the particles with high transversal moment (high-Pt

particles).

The muon system is used to identify and trigger on muons in the events.

LHCb Physics analyses

After the LHC starts colliding protons at a useful rate for LHCb, in early 2010, LHCb aims to make several

measurements on physics phenomena involving B mesons as an early priority. These include:

• Measuring an upper limit on the branching ratio of the rare decay.• Measuring the forward-backward asymmetry of the muon pair in the flavour changing neutral current

decay. Such a flavour changing neutral current cannot occur at tree-level in the Standard

Model of Particle Physics, and only occurs through box and loop Feynman diagrams; properties of the decay canbe strongly modified by new Physics.• Measuring the CP violating phase in the decay , caused by interference between the decays with

and without oscillations. This phase is one of the CP observables with the smallest theoretical

uncertainty in the Standard Model, and can be significantly modified by new Physics.• Measuring properties of radiative B decays, i.e. B meson decays with photons in the final states. Specifically,

these are again flavour changing neutral current decays.

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LHCb 48

See also

• CERN: European Organization for Nuclear Research

• Large Hadron Collider

External links

• LHCb Public Webpage [1]

• LHCb section from US/LHC Website [2]

• A. Augusto Alves Jr. et al. (LHCb Collaboration) (2008). "The LHCb Detector at the LHC" [5]. Journal of 

 Instrumentation 3: S08005. doi:10.1088/1748-0221/3/08/S08005. (Full design documentation)

References

[1] http://lhcb-public. web. cern. ch/lhcb-public/ 

[2] http://www. uslhc. us/What_is_the_LHC/Experiments/LHCb

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LHCf  49

LHCf 

The LHCf experiment, the smallest of the six

experiments on the LHC

LHC experiments

ATLAS A Toroidal LHC Apparatus

CMS Compact Muon Solenoid

LHCb LHC-beauty

ALICE A Large Ion Collider Experiment

TOTEM Total Cross Section, Elastic Scattering and Diffraction Dissociation

LHCf  LHC-forward

MoEDAL Monopole and Exotics Detector At the LHC

LHC preaccelerators

p and Pb Linear accelerators for protons (Linac 2) and Lead (Linac 3)

(not marked) Proton Synchrotron Booster

PS Proton Synchrotron

SPS Super Proton Synchrotron

The LHCf  ("Large Hadron Collider forward") is a special-purpose Large Hadron Collider experiment for

astroparticle (cosmic ray) physics, and one of six detectors being constructed in the LHC accelerator at CERN. The

other five are: ATLAS, ALICE, CMS, TOTEM, and LHCb. LHCf is designed to study the particles generated in the

"forward" region of collisions, those almost directly in line with the colliding proton beams. It therefore consists of 

two detectors, 140 m on either side of an intersection point.

Because of this large distance, it can co-exist with a more conventional detector surrounding the intersection point,

and shares the intersection point IP1 with the much larger general-purpose ATLAS experiment.

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LHCf  50

Purpose

The LHCf is intended to measure the energy and numbers of neutral pions (π0) produced by the collider. This will

hopefully help explain the origin of ultra-high energy cosmic rays. The results will complement other high-energy

cosmic ray measurements from the Pierre Auger Observatory in Argentina, and the Telescope Array in Utah.

References

• LHCf section on US/LHC Website [1]

• LHCf: a tiny new experiment joins the LHC [2], CERN Courier, Nov 1, 2006, retrieved on 2009-03-25.

(Describes the location of the experiment.)

• The LHCf experiment at LHC [3]

• Technical Design Report of LHCf [4]

• O Adriani et al. (LHCf Collaboration) (2008). "The LHCf detector at the CERN Large Hadron Collider". Journal

of Instrumentation 3 (8): S08006. doi:10.1088/1748-0221/3/08/S08006. (Full design documentation)

References[1] http://www. uslhc. us/What_is_the_LHC/Experiments/LHCf 

[2] http://cerncourier. com/cws/article/cern/29732

[3] http://www. particle. cz/conferences/c2cr2005/talks/Adriani.pdf 

[4] http://doc. cern. ch//archive/electronic/cern/preprints/lhcc/public/lhcc-2005-032.pdf 

FP420

The FP420 R&D project or the FP420 experiment was an international collaboration with members from 29

institutes from 10 countries.[1] The aim was to assess the feasibility of installing proton tagging detectors at 420 m

from the interaction points of the ATLAS and CMS experiments at the Large Hadron Collider (LHC). One of the

most notable members of the team was Brian Cox, who can be seen in the five part BBC television series entitled

Wonders of the Solar System which first aired in March 2010.

By detecting protons that have lost less than 1% of their longitudinal momentum, it is possible to obtain information

that could yield insight on various phenomena of high-energy physics. These measurements would be unique at the

LHC, and would be difficult to obtain at both existing and future linear colliders.

See also

• List of Large Hadron Collider experiments

References

[1] "FP420 R&D Project" (http://www. fp420.  com/). . Retrieved 2010-03-31.

External links

• FP420 R&D Project website (http://www. fp420. com/)

• Papers and Reviews (http://www. fp420. com/papers. html)

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TOTEM 51

TOTEM

LHC experiments

ATLAS A Toroidal LHC Apparatus

CMS Compact Muon Solenoid

LHCb LHC-beauty

ALICE A Large Ion Collider Experiment

TOTEM Total Cross Section, Elastic Scattering and Diffraction Dissociation

LHCf  LHC-forward

MoEDAL Monopole and Exotics Detector At the LHC

LHC preaccelerators

p and Pb Linear accelerators for protons (Linac 2) and Lead (Linac 3)

(not marked) Proton Synchrotron Booster

PS Proton Synchrotron

SPS Super Proton Synchrotron

TOTal Elastic and diffractive cross section Measurement (TOTEM) is one of the six detector experiments being

constructed at the Large Hadron Collider at CERN. The other five are: ATLAS, ALICE, CMS, LHCb, and LHCf. It

shares intersection point IP5 with the Compact Muon Solenoid. The detector aims at measurement of total cross

section, elastic scattering and diffractive processes.

See also

• CERN: European Organization for Nuclear Research

• Large Hadron Collider

External links

• TOTEM Public Webpage [1]

• TOTEM section on US/LHC Website [2]

• The TOTEM Collaboration, G Anelli et al. (2008-08-14), "The TOTEM Experiment at the CERN Large Hadron

Collider" [5], Journal of Instrumentation 3 (S08007): S08007, doi:10.1088/1748-0221/3/08/S08007, retrieved

2008-08-26 (Full design documentation)

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TOTEM 52

References

[1] http://totem. web. cern. ch/Totem

[2] http://www. uslhc. us/What_is_the_LHC/Experiments/TOTEM

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53

Technology

LHC Computing GridThe LHC Computing Grid, launched on October 3, 2008,[1] is a distribution network designed by CERN to handle

the massive amounts of data produced by the Large Hadron Collider (LHC). It incorporates both private fiber optic

cable links and existing high-speed portions of the public Internet.

The data stream from the detectors provides approximately 300 GB/s, which is filtered for "interesting events",

resulting in a "raw data" stream of about 300 MB/s. The CERN computer center, considered "Tier 0" of the LHC

Computing Grid, has a dedicated 10 Gb/s connection to the counting room.[2]

The project is expected to generate 27 TB of raw data per day, plus 10 TB of “event summary data”, which represents

the output of calculations done by the CPU farm at the CERN data center. [2] This data is sent out from CERN to

eleven Tier 1 academic institutions in Europe, Asia, and North America, via dedicated 10 Gbit/s links. More than150 Tier 2 institutions are connected to the Tier 1 institutions by general-purpose national research and education

networks.[2] The data produced by the LHC on all of its distributed computing grid is expected to add up to 10 –15

PB of data each year.[3]

The Tier 1 institutions receive specific subsets of the raw data, for which they serve as a backup repository for

CERN. They also perform reprocessing when recalibration is necessary.[2] The primary configuration for the

computers used in the grid is based on Scientific Linux.

Distributed computing resources for analysis by end-user physicists are provided by the Open Science Grid,

Enabling Grids for E-sciencE,[2] and LHC@home projects.

See also

• Openlab (CERN)

References

[1] "LHC GridFest" (http://lcg. web. cern.ch/LCG/lhcgridfest/). CERN. 2008. .

[2] final-draft-4-key (http://gridcafe.web.cern. ch/gridcafe/animations/LHCdata/LHCdata. html)

[3] Brodkin, Jon (28 April 2008). "Parallel Internet: Inside the Worldwide LHC computing grid" (http://www. techworld. com/mobility/ 

features/index. cfm?featureid=4074&pn=2). Techworld.com. .

External links

• Official webpage (http://lcg.web. cern. ch/LCG/) The World Wide LHC Computer Grid

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LHC@home 54

LHC@home

LHC@home is a distributed computing project using the BOINC framework, run by volunteers for the CERN in

Switzerland. Its goal is to help maintain and improve the Large Hadron Collider (LHC), a CERN project to create a

large particle accelerator which became active in September 2008. Data from the project is used by engineers to

improve the operation and efficiency of the accelerator, and to predict problems that could arise from adjustment ormodification of the LHC's equipment. The project is administered by volunteers, and receives no funding from

CERN.

BOINC users who are considering joining this project should know that it only occasionally has work; the project is

used for design and repair considerations related to the LHC. There are currently no plans to use the project to do

computation on the data that will be collected by the LHC.

A CERN collider project

The project was first introduced as a beta on September 1, 2004 and a record 1000 users signed up within 24 hours.

The project went public, with a 5000 user limit, on September 29 to commemorate CERN's 50th anniversary.Currently there is no user limit and qualification.

Project software

The project software involves a program called "SixTrack", created by Frank Schmidt, downloaded via BOINC onto

participant computers running Windows or Linux. SixTrack simulates particles accelerating through the 27 km (17

mi)-long LHC to find their orbit stability.

• In one workunit, 60 particles are simulated travelling 100,000 or 1,000,000 loops, which would take about 10

seconds in an actual run. This is sixtrack.

• The orbit stability data is used to detect if a particle in orbit goes off-course and runs into the tube wall —if this

happened too often in actual running, this would cause damage to the accelerator which would need repairs.

• A new experimental version called SixTrackbnl started to be sent to computers in early November.

• Garfield is a newer application, although not many workunits have been seen lately.

See also

• List of distributed computing projects

• LHC Computing Grid

External links

• LHC@home Project Page [1]

• Berkeley Open Infrastructure for Network Computing (BOINC) [2]

• SixTrack homepage [3]

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LHC@home 55

References

[1] http://lhcathome. cern. ch/ 

[2] http://boinc. berkeley. edu/ 

[3] http://frs. web. cern. ch/frs/ 

Proton Synchrotron BoosterThe Proton Synchrotron Booster, a synchrotron, is the first and smallest circular proton accelerator in the

accelerator chain at the CERN Large Hadron Collider injection complex[1]. The accelerator was built in 1972, and

contains four superimposed rings with a radius of 25 meters. It takes protons with an energy of 50 MeV from the

linear accelerator Linac2 and accelerates them up to 1.4 GeV, ready to be injected into the Proton Synchrotron. It can

also take ions from the Linac3 pre-accelerated in the LEIR.

The PS Booster actually consists of four identical rings mounted one above the other.

External links• PS Booster Machine: layout and photographs [2]

References

[1] http://ps-div. web. cern. ch/ps-div/LHC-PS/LHC-PS.html

[2] http://psb-machine. web. cern.ch/psb-machine/ 

VELO

The Vertex Locator at LHCb is called the VELO. Its primary purpose is to provide high precision measurements of 

the tracks of charged particles resulting from pp collisions at the LHC.

The detector operates at 7 mm from the LHC beam. This implies an enormous flux of particles; thus the VELO has

been designed to withstand integrated fluences of more than 1014p/cm2 per year for a period of about three years.

The detector operates in vacuum and is cooled to approximately −25 °C using a biphase CO2

system. The data of the

VELO detector are amplified and read out by the Beetle ASIC.

The VELO provides critical tracking information for the LHCb experiment.

References

• The LHCb VELO (from the VELO group) [1]

• VELO Public Pages(from the LHCb experiment) [2]

References

[1] http://lhcb-vd. web. cern. ch/lhcb-vd/default. htm

[2] http://lhcb-public. web. cern. ch/lhcb-public/en/Detector/VELO-en.html

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56

Theory

Standard Model

The Standard Model of elementary particles, with the gauge bosons in the

rightmost column.

The Standard Model of particle physics is

a theory concerning the electromagnetic,

weak, and strong nuclear interactions, which

mediate the dynamics of the known

subatomic particles. Developed throughout

the early and middle 20th century, the

current formulation was finalized in the mid

1970s upon experimental confirmation of 

the existence of quarks. Since then,discoveries of the bottom quark (1977), the

top quark (1995) and the tau neutrino (2000)

have given credence to the standard model.

Because of its success in explaining a wide

variety of experimental results, the standard

model is sometimes regarded as a theory of 

almost everything.

Still, the standard model falls short of being

a complete theory of fundamentalinteractions because it does not incorporate

the physics of general relativity, such as

gravitation and dark energy. The theory

does not contain any viable dark matter

particle that possesses all of the required properties deduced from observational cosmology. It also does not correctly

account for neutrino oscillations (and their non-zero masses). Although the standard model is theoretically

self-consistent, it has several unnatural properties giving rise to puzzles like the strong CP problem and the hierarchy

problem.

Nevertheless, the standard model is important to theoretical and experimental particle physicists alike. For

theoreticians, the standard model is a paradigm example of a quantum field theory, which exhibits a wide range of physics including spontaneous symmetry breaking, anomalies, non-perturbative behavior, etc. It is used as a basis for

building more exotic models which incorporate hypothetical particles, extra dimensions and elaborate symmetries

(such as supersymmetry) in an attempt to explain experimental results at variance with the Standard Model such as

the existence of dark matter and neutrino oscillations. In turn, the experimenters have incorporated the standard

model into simulators to help search for new physics beyond the standard model from relatively uninteresting

background.

Recently, the standard model has found applications in other fields besides particle physics such as astrophysics and

cosmology, in addition to nuclear physics.

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Standard Model 57

Historical background

The first step towards the Standard Model was Sheldon Glashow's discovery, in 1960, of a way to combine the

electromagnetic and weak interactions.[1] In 1967, Steven Weinberg[2] and Abdus Salam[3] incorporated the Higgs

mechanism[4] [5] [6] into Glashow's electroweak theory, giving it its modern form.

The Higgs mechanism is believed to give rise to the masses of all the elementary particles in the Standard Model.

This includes the masses of the W and Z bosons, and the fermions. The Higgs mechanism is also believed to giverise to the masses of quarks and leptons.

After the neutral weak currents caused by Z boson exchange were discovered at CERN in 1973, [7]  [8]  [9]  [10] the

electroweak theory became widely accepted and Glashow, Salam, and Weinberg shared the 1979 Nobel Prize in

Physics for discovering it. The W and Z bosons were discovered experimentally in 1981, and their masses were

found to be as the Standard Model predicted.

The theory of the strong interaction, to which many contributed, acquired its modern form around 1973 –74, when

experiments confirmed that the hadrons were composed of fractionally charged quarks.

OverviewAt present, matter and energy are best understood in terms of the kinematics and interactions of elementary particles.

To date, physics has reduced the laws governing the behavior and interaction of all known forms of matter and

energy to a small set of fundamental laws and theories. A major goal of physics is to find the "common ground" that

would unite all of these theories into one integrated theory of everything, of which all the other known laws would

be special cases, and from which the behavior of all matter and energy could be derived (at least in principle).[11]

The Standard Model groups two major extant theories  — quantum electroweak and quantum chromodynamics —

into an internally consistent theory that describes the interactions between all known particles in terms of quantum

field theory. For a technical description of the fields and their interactions, see Standard Model (mathematical

formulation).

Particle content

Elementary particles: fermions

Organization of Fermions

Charge First generation Second generation Third generation

Quarks +2 ⁄ 3

Up u Charm c Top t

−1 ⁄ 3

Down d Strange s Bottom b

Leptons −1 Electron e− Muon μ− Tau τ−

0 Electron neutrino νe

Muon neutrino νμ

Tau neutrino ντ

The Standard Model includes 12 elementary particles of spin-1 ⁄ 2

known as fermions. According to the spin-statistics

theorem, fermions respect the Pauli exclusion principle. Each fermion has a corresponding antiparticle.

The fermions of the Standard Model are classified according to how they interact (or equivalently, by what charges

they carry). There are six quarks (up, down, charm, strange, top, bottom), and six leptons (electron, electron

neutrino, muon, muon neutrino, tau, tau neutrino). Pairs from each classification are grouped together to form a

generation, with corresponding particles exhibiting similar physical behavior (see table).

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Standard Model 58

The defining property of the quarks is that they carry color charge, and hence, interact via the strong interaction. A

phenomenon called color confinement results in quarks being perpetually (or at least since very soon after the start of 

the Big Bang) bound to one another, forming color-neutral composite particles (hadrons) containing either a quark

and an antiquark (mesons) or three quarks (baryons). The familiar proton and the neutron are the two baryons having

the smallest mass. Quarks also carry electric charge and weak isospin. Hence they interact with other fermions both

electromagnetically and via the weak nuclear interaction.

The remaining six fermions do not carry color charge and are called leptons. The three neutrinos do not carry electric

charge either, so their motion is directly influenced only by the weak nuclear force, which makes them notoriously

difficult to detect. However, by virtue of carrying an electric charge, the electron, muon, and tau all interact

electromagnetically.

Each member of a generation has greater mass than the corresponding particles of lower generations. The first

generation charged particles do not decay; hence all ordinary (baryonic) matter is made of such particles.

Specifically, all atoms consist of electrons orbiting atomic nuclei ultimately constituted of up and down quarks.

Second and third generations charged particles, on the other hand, decay with very short half lives, and are observed

only in very high-energy environments. Neutrinos of all generations also do not decay, and pervade the universe, but

rarely interact with baryonic matter.

Force mediating particles

Summary of interactions between particles described by the Standard Model.

Interactions in physics are the ways

that particles influence other particles.

At a macroscopic level,

electromagnetism allows particles to

interact with one another via electric

and magnetic fields, and gravitation

allows particles with mass to attractone another in accordance with

Einstein's general relativity. The

standard model explains such forces as

resulting from matter particles

exchanging other particles, known as

  force mediating particles (Strictly

speaking, this is only so if interpreting

literally what is actually an

approximation method  known as

perturbation theory, as opposed to theexact theory). When a force mediating particle is exchanged, at a macroscopic level the effect is equivalent to a force

influencing both of them, and the particle is therefore said to have mediated (i.e., been the agent of) that force. The

Feynman diagram calculations, which are a graphical form of the perturbation theory approximation, invoke "force

mediating particles" and when applied to analyze high-energy scattering experiments are in reasonable agreement

with the data. Perturbation theory (and with it the concept of "force mediating particle") in other situations fails.

These include low-energy QCD, bound states, and solitons.

The known force mediating particles described by the Standard Model also all have spin (as do matter particles), but

in their case, the value of the spin is 1, meaning that all force mediating particles are bosons. As a result, they do not

follow the Pauli exclusion principle. The different types of force mediating particles are described below.

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Standard Model 59

• Photons mediate the electromagnetic force between electrically charged particles. The photon is massless and is

well-described by the theory of quantum electrodynamics.

• The W+, W−, and Z gauge bosons mediate the weak interactions between particles of different flavors (all quarks

and leptons). They are massive, with the Z being more massive than the W±. The weak interactions involving the

W± act on exclusively left-handed particles and right-handed antiparticles. Furthermore, the W± carry an electric

charge of +1 and −1 and couple to the electromagnetic interactions. The electrically neutral Z boson interacts withboth left-handed particles and antiparticles. These three gauge bosons along with the photons are grouped together

which collectively mediate the electroweak interactions.

• The eight gluons mediate the strong interactions between color charged particles (the quarks). Gluons are

massless. The eightfold multiplicity of gluons is labeled by a combination of color and an anticolor charge (e.g.,

red –antigreen).[12] Because the gluon has an effective color charge, they can interact among themselves. The

gluons and their interactions are described by the theory of quantum chromodynamics.

The interactions between all the particles described by the Standard Model are summarized by the diagram at the top

of this section.

The Higgs boson

The Higgs particle is a hypothetical massive scalar elementary particle theorized by Robert Brout, François Englert,

Peter Higgs, Gerald Guralnik, C. R. Hagen, and Tom Kibble in 1964 (see 1964 PRL symmetry breaking papers) and

is a key building block in the Standard Model.[13] [14] [15] [16] It has no intrinsic spin, and for that reason is classified

as a boson (like the force mediating particles, which have integer spin). Because an exceptionally large amount of 

energy and beam luminosity are theoretically required to observe a Higgs boson in high energy colliders, it is the

only fundamental particle predicted by the Standard Model that has yet to be observed.

The Higgs boson plays a unique role in the Standard Model, by explaining why the other elementary particles, the

photon and gluon excepted, are massive. In particular, the Higgs boson would explain why the photon has no mass,

while the W and Z bosons are very heavy. Elementary particle masses, and the differences betweenelectromagnetism (mediated by the photon) and the weak force (mediated by the W and Z bosons), are critical to

many aspects of the structure of microscopic (and hence macroscopic) matter. In electroweak theory, the Higgs

boson generates the masses of the leptons (electron, muon, and tau) and quarks.

As yet, no experiment has directly detected the existence of the Higgs boson. It is hoped that the Large Hadron

Collider at CERN will confirm the existence of this particle. It is also possible that the Higgs boson may already

have been produced but overlooked.[17]

Field content

The standard model has the following fields:

Spin 1

1. A U(1) gauge field B μν

with coupling g′ (weak U(1), or weak hypercharge)

2. An SU(2) gauge field W  μν

with coupling g (weak SU(2), or weak isospin)

3. An SU(3) gauge field G μν

with coupling gs

(strong SU(3), or color charge)

Spin1 ⁄ 

2

The spin 1 ⁄ 2

particles are in representations of the gauge groups. For the U(1) group, we list the value of the weak

hypercharge instead. The left-handed fermionic fields are:

1. An SU(3) triplet, SU(2) doublet, with U(1) weak hypercharge 1 ⁄ 3

(left-handed quarks)

2. An SU(3) triplet, SU(2) singlet, with U(1) weak hypercharge 2 ⁄ 3

(left-handed down-type antiquark)

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Standard Model 60

3. An SU(3) singlet, SU(2) doublet with U(1) weak hypercharge −1 (left-handed lepton)

4. An SU(3) triplet, SU(2) singlet, with U(1) weak hypercharge −4 ⁄ 3

(left-handed up-type antiquark)

5. An SU(3) singlet, SU(2) singlet with U(1) weak hypercharge 2 (left-handed antilepton)

By CPT symmetry, there is a set of right-handed fermions with the opposite quantum numbers.

This describes one generation of leptons and quarks, and there are three generations, so there are three copies of each

field. Note that there are twice as many left-handed lepton field components as left-handed antilepton fieldcomponents in each generation, but an equal number of left-handed quark and antiquark fields.

Spin 0

1. An SU(2) doublet H with U(1) hyper-charge −1 (Higgs field)

Note that | H |2, summed over the two SU(2) components, is invariant under both SU(2) and under U(1), and so it can

appear as a renormalizable term in the Lagrangian, as can its square.

This field acquires a vacuum expectation value, leaving a combination of the weak isospin, I3, and weak hypercharge

unbroken. This is the electromagnetic gauge group, and the photon remains massless. The standard formula for the

electric charge (which defines the normalization of the weak hypercharge, Y , which would otherwise be somewhatarbitrary) is:[18]

Lagrangian

The Lagrangian for the spin 1 and spin 1 ⁄ 2

fields is the most general renormalizable gauge field Lagrangian with no

fine tunings:

• Spin 1:

where the traces are over the SU(2) and SU(3) indices hidden in W and G respectively. The two-index objects are the

field strengths derived from W and G the vector fields. There are also two extra hidden parameters: the theta angles

for SU(2) and SU(3).

The spin-1 ⁄ 2

particles can have no mass terms because there is no right/left helicity pair with the same SU(2) and

SU(3) representation and the same weak hypercharge. This means that if the gauge charges were conserved in the

vacuum, none of the spin 1 ⁄ 2

particles could ever swap helicity, and they would all be massless.

For a neutral fermion, for example a hypothetical right-handed lepton  N (or  N α in relativistic two-spinor notation),

with no SU(3), SU(2) representation and zero charge, it is possible to add the term:

This term gives the neutral fermion a Majorana mass. Since the generic value for M will be of order 1, such a particle

would generically be unacceptably heavy. The interactions are completely determined by the theory  – the leptons

introduce no extra parameters.

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Standard Model 61

Higgs mechanism

The Lagrangian for the Higgs includes the most general renormalizable self interaction:

The parameter v2 has dimensions of mass squared, and it gives the location where the classical Lagrangian is at a

minimum. In order for the Higgs mechanism to work, v2 must be a positive number. v has units of mass, and it is theonly parameter in the standard model which is not dimensionless. It is also much smaller than the Planck scale; it is

approximately equal to the Higgs mass, and sets the scale for the mass of everything else. This is the only real

fine-tuning to a small nonzero value in the standard model, and it is called the Hierarchy problem.

It is traditional to choose the SU(2) gauge so that the Higgs doublet in the vacuum has expectation value (v,0).

Masses and CKM matrix

The rest of the interactions are the most general spin-0 spin-1 ⁄ 2

Yukawa interactions, and there are many of these.

These constitute most of the free parameters in the model. The Yukawa couplings generate the masses and mixings

once the Higgs gets its vacuum expectation value.The terms L

* HR generate a mass term for each of the three generations of leptons. There are 9 of these terms, but by

relabeling L and R, the matrix can be diagonalized. Since only the upper component of  H  is nonzero, the upper

SU(2) component of  L mixes with  R to make the electron, the muon, and the tau, leaving over a lower massless

component, the neutrino. {Neutrino oscillation show neutrinos have mass. http:/ / operaweb.  lngs.  infn.  it/ spip.

php?rubrique14 31May2010 Press Release.}

The terms QHU generate up masses, while QHD generate down masses. But since there is more than one

right-handed singlet in each generation, it is not possible to diagonalize both with a good basis for the fields, and

there is an extra CKM matrix.

Theoretical aspects

Construction of the Standard Model Lagrangian

Parameters of the Standard Model

Symbol Description Renormalization

scheme (point)

Value

me

Electron mass 511 keV

mμ

Muon mass 105.7 MeV

mτ

Tau mass 1.78 GeV

mu

Up quark mass  μMS

= 2 GeV 1.9 MeV

md

Down quark mass  μMS

= 2 GeV 4.4 MeV

ms

Strange quark mass  μMS

= 2 GeV 87 MeV

mc

Charm quark mass  μMS

= mc

1.32 GeV

mb

Bottom quark mass  μMS

= mb

4.24 GeV

mt

Top quark mass On-shell scheme 172.7 GeV

θ12

CKM 12-mixing angle 13.1°

θ23

CKM 23-mixing angle 2.4°

θ13

CKM 13-mixing angle 0.2°

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Standard Model 62

δ CKM CP-violating Phase 0.995

g1

U(1) gauge coupling  μMS

= mZ

0.357

g2

SU(2) gauge coupling  μMS

= mZ

0.652

g3

SU(3) gauge coupling  μMS

= mZ

1.221

θ

QCD

QCD vacuum angle ~0

 μ Higgs quadratic coupling Unknown

 λ Higgs self-coupling strength Unknown

Technically, quantum field theory provides the mathematical framework for the standard model, in which a

Lagrangian controls the dynamics and kinematics of the theory. Each kind of particle is described in terms of a

dynamical field that pervades space-time. The construction of the standard model proceeds following the modern

method of constructing most field theories: by first postulating a set of symmetries of the system, and then by writing

down the most general renormalizable Lagrangian from its particle (field) content that observes these symmetries.

The global Poincaré symmetry is postulated for all relativistic quantum field theories. It consists of the familiar

translational symmetry, rotational symmetry and the inertial reference frame invariance central to the theory of special relativity. The local SU(3)×SU(2)×U(1) gauge symmetry is an internal symmetry that essentially defines the

standard model. Roughly, the three factors of the gauge symmetry give rise to the three fundamental interactions.

The fields fall into different representations of the various symmetry groups of the Standard Model (see table). Upon

writing the most general Lagrangian, one finds that the dynamics depend on 19 parameters, whose numerical values

are established by experiment. The parameters are summarized in the table at right.

The QCD sector

The QCD sector defines the interactions between quarks and gluons, with SU(3) symmetry, generated by T a. Since

leptons do not interact with gluons, they are not affected by this sector.

is the gluon field strength, are the Dirac matrices, D stands for the isospin doublet section, U stands for a

unitary matrix, and gs

is the strong coupling constant.

The electroweak sector

The electroweak sector is a Yang –Mills gauge theory with the symmetry group U(1)×SU(2)L,

where  B μ

is the U(1) gauge field; Y W

is the weak hypercharge  — the generator of the U(1) group; is the

three-component SU(2) gauge field; are the Pauli matrices — infinitesimal generators of the SU(2) group. The

subscript L indicates that they only act on left fermions; g′ and g are coupling constants.

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Standard Model 63

The Higgs sector

In the Standard Model, the Higgs field is a complex spinor of the group SU(2)L:

where the indexes + and 0 indicate the electric charge (Q) of the components. The weak isospin (Y W

) of both

components is 1.

Before symmetry breaking, the Higgs Lagrangian is:

which can also be written as:

Additional symmetries of the Standard Model

From the theoretical point of view, the Standard Model exhibits four additional global symmetries, not postulated at

the outset of its construction, collectively denoted accidental symmetries, which are continuous U(1) global

symmetries. The transformations leaving the Lagrangian invariant are:

The first transformation rule is shorthand meaning that all quark fields for all generations must be rotated by an

identical phase simultaneously. The fields , and , are the 2nd (muon) and 3rd (tau)

generation analogs of and fields.

By Noether's theorem, each symmetry above has an associated conservation law: the conservation of baryon number,

electron number, muon number, and tau number. Each quark is assigned a baryon number of 1/3, while each

antiquark is assigned a baryon number of -1/3. Conservation of baryon number implies that the number of quarks

minus the number of antiquarks is a constant. Within experimental limits, no violation of this conservation law has

been found.

Similarly, each electron and its associated neutrino is assigned an electron number of +1, while the antielectron and

the associated antineutrino carry −1 electron number. Similarly, the muons and their neutrinos are assigned a muon

number of +1 and the tau leptons are assigned a tau lepton number of +1. The Standard Model predicts that each of 

these three numbers should be conserved separately in a manner similar to the way baryon number is conserved.

These numbers are collectively known as lepton family numbers (LF). Symmetry works differently for quarks than

for leptons, mainly because the Standard Model predicts that neutrinos are massless. However, it was recently found

that neutrinos have small masses and oscillate between flavors, signaling that the conservation of lepton family

number is violated.In addition to the accidental (but exact) symmetries described above, the Standard Model exhibits several

approximate symmetries. These are the "SU(2) custodial symmetry" and the "SU(2) or SU(3) quark flavor

symmetry."

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Standard Model 64

Symmetries of the Standard Model and Associated Conservation Laws

Symmetry Lie Group Symmetry Type Conservation Law

Poincaré Translations×SO(3,1) Global symmetry Energy, Momentum, Angular momentum

Gauge SU(3)×SU(2)×U(1) Local symmetry Color charge, Weak isospin, Electric charge, Weak hypercharge

Baryon phase U(1) Accidental Global symmetry Baryon numberElectron phase U(1) Accidental Global symmetry Electron number

Muon phase U(1) Accidental Global symmetry Muon number

Tau phase U(1) Accidental Global symmetry Tau number

Field content of the Standard Model

Field

(1st generation)

Spin Gauge group

Representation

Baryon

Number

Electron

Number

Left-handed quark ( , , )

Left-handed up antiquark ( , , )

Left-handed down antiquark ( , , )

Left-handed lepton ( , , )

Left-handed antielectron ( , , )

Hypercharge gauge field ( , , )

Isospin gauge field ( , , )

Gluon field ( , , )

Higgs field ( , , )

List of standard model fermions

This table is based in part on data gathered by the Particle Data Group.[19]

Left-handed fermions in the Standard Model

Generation 1

Fermion

(left-handed)

Symbol Electric

charge

Weak

isospin

Weak

hypercharge

Color

charge *

Mass **

Electron 511 keVPositron 511 keV

Electron neutrino < 2 eV ****

Electron antineutrino < 2 eV ****

Up quark ~ 3 MeV ***

Up antiquark ~ 3 MeV ***

Down quark ~ 6 MeV ***

Down antiquark ~ 6 MeV ***

Generation 2

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Standard Model 65

Fermion

(left-handed)

Symbol Electric

charge

Weak

isospin

Weak

hypercharge

Color

charge *

Mass **

Muon 106 MeV

Antimuon 106 MeV

Muon neutrino < 2 eV ****

Muon antineutrino < 2 eV ****

Charm quark ~ 1.337 GeV

Charm antiquark ~ 1.3 GeV

Strange quark ~ 100 MeV

Strange antiquark ~ 100 MeV

Generation 3

Fermion

(left-handed)

Symbol Electric

charge

Weak

isospin

Weak

hypercharge

Color

charge *

Mass **

Tau 1.78 GeV

Antitau 1.78 GeV

Tau neutrino < 2 eV ****

Tau antineutrino < 2 eV ****

Top quark 171 GeV

Top antiquark 171 GeV

Bottom quark ~ 4.2 GeV

Bottom antiquark ~ 4.2 GeV

Notes:• * These are not ordinary abelian charges, which can be added together, but are labels of group representations of Lie groups.

• ** Mass is really a coupling between a left-handed fermion and a right-handed fermion. For example, the mass of an electron is really a

coupling between a left-handed electron and a right-handed electron, which is the antiparticle of a left-handed positron. Also neutrinos show

large mixings in their mass coupling, so it's not accurate to talk about neutrino masses in the flavor basis or to suggest a left-handed electron

antineutrino.

• *** The masses of baryons and hadrons and various cross-sections are the experimentally measured quantities. Since quarks can't be isolated

because of QCD confinement, the quantity here is supposed to be the mass of the quark at the renormalization scale of the QCD scale.

• **** The Standard Model assumes that neutrinos are massless. However, several contemporary experiments prove that neutrinos oscillate

between their flavour states, which could not happen if all were massless.[20]

It is straightforward to extend the model to fit these data but there

are many possibilities, so the mass eigenstates are still open. See Neutrino#Mass.

Log plot of masses in the Standard Model.

Tests and predictions

The Standard Model (SM) predicted

the existence of the W and Z bosons,

gluon, and the top and charm quarks

before these particles were observed.

Their predicted properties were

experimentally confirmed with good

precision. To give an idea of the

success of the SM, the following table compares the measured masses of the W and Z bosons with the massespredicted by the SM:

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Standard Model 66

Quantity Measured (GeV) SM prediction (GeV)

Mass of W boson 80.398 ± 0.025 80.390 ± 0.018

Mass of Z boson 91.1876 ± 0.0021 91.1874 ± 0.0021

The SM also makes several predictions about the decay of Z bosons, which have been experimentally confirmed by

the Large Electron-Positron Collider at CERN.

Challenges to the standard model

There is some experimental evidence consistent with neutrinos having mass, which the Standard Model does not

allow.[21] To accommodate such findings, the Standard Model can be modified by adding a non-renormalizable

interaction of lepton fields with the square of the Higgs field. This is natural in certain grand unified theories, and if 

new physics appears at about 1016 GeV, the neutrino masses are of the right order of magnitude.

Currently, there is one elementary particle predicted by the Standard Model that has yet to be observed: the Higgs

boson. A major reason for building the Large Hadron Collider is that the high energies of which it is capable are

expected to make the Higgs observable. However, as of August 2008, there is only indirect empirical evidence forthe existence of the Higgs boson, so that its discovery cannot be claimed. Moreover, there are serious theoretical

reasons for supposing that elementary scalar Higgs particles cannot exist (see Quantum triviality).

A fair amount of theoretical and experimental research has attempted to extend the Standard Model into a Unified

Field Theory or a Theory of everything, a complete theory explaining all physical phenomena including constants.

Inadequacies of the Standard Model that motivate such research include:

• Does not attempt to explain gravitation, and there is no known way of adapting the quantum field theory of the

sort the Standard Model employs freely, with general relativity, the canonical theory of gravitation. This means,

among other things, that we have no good theory for the very early universe;

• Seems rather ad-hoc and inelegant, requiring 19 numerical constants whose values are unrelated and arbitrary.Although the Standard Model, as it now stands, cannot explain why neutrinos have masses (and the specifics of 

neutrino mass are still unclear), it is believed that explaining neutrino mass will require an additional 7 or 8

constants;

• Gives rise to the hierarchy problem, namely why the weak scale and Planck scale are so disparate;

• Should be modified so as to be consistent with the emerging "standard model of cosmology." Specifically, a truly

satisfactory theory of the elementary particles and of the fundamental interactions must explain the initial

conditions of the universe that gave rise to certain observed properties of the present-day universe, properties such

as the predominance of matter over antimatter (matter/antimatter asymmetry), and its isotropy and homogeneity

over large distances.

It should be remarked that neither Unified Field Theory nor the Theory of everything are presently able to addressand solve these problems in conclusive ways.

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Standard Model 67

See also

• Elementary particle:

• Boson, Fermion

• Fundamental interaction:

• Quantum electrodynamics

• Strong interaction:

• Color charge, Quantum chromodynamics, Quark model

• Weak interaction:

• Electroweak theory, Fermi theory of beta decay, Weak hypercharge, Weak isospin

• Gauge theory

• Nontechnical introduction to gauge theory

• Open questions: BTeV experiment, CP violation, Neutrino masses, Quark matter

• Quantum field theory

• Standard Model:

• Beyond the...

• Mathematical formulation of 

• Diagrams:

• Feynman

• Penguin

• Flavour

• Generation

• Higgs mechanism

• Higgs boson

• Unparticle physics• 1964 PRL symmetry breaking papers

• Lagrangian

• Noncommutative standard model

• J. J. Sakurai Prize for Theoretical Particle Physics

• C.R. Hagen

Notes and references

Notes

[1] S.L. Glashow (1961). "Partial-symmetries of weak interactions". Nuclear Physics  22: 579 –588. doi:10.1016/0029-5582(61)90469-2.[2] S. Weinberg (1967). "A Model of Leptons". Physical Review Letters 19: 1264 –1266. doi:10.1103/PhysRevLett.19.1264.

[3] A. Salam (1968). N. Svartholm. ed. Elementary Particle Physics: Relativistic Groups and Analyticity. Eighth Nobel Symposium. Stockholm:

Almquvist and Wiksell. pp. 367.

[4] F. Englert, R. Brout (1964). "Broken Symmetry and the Mass of Gauge Vector Mesons". Physical Review Letters 13: 321 –323.

doi:10.1103/PhysRevLett.13.321.

[5] P.W. Higgs (1964). "Broken Symmetries and the Masses of Gauge Bosons". Physical Review Letters 13: 508 –509.

doi:10.1103/PhysRevLett.13.508.

[6] G.S. Guralnik, C.R. Hagen, T.W.B. Kibble (1964). "Global Conservation Laws and Massless Particles". Physical Review Letters 13:

585 –587. doi:10.1103/PhysRevLett.13.585.

[7] F.J. Hasert et al. (1973). "Search for elastic muon-neutrino electron scattering". Physics Letters B 46: 121.

doi:10.1016/0370-2693(73)90494-2.

[8] F.J. Hasert et al. (1973). "Observation of neutrino-like interactions without muon or electron in the gargamelle neutrino experiment". Physics

 Letters B 46: 138. doi:10.1016/0370-2693(73)90499-1.

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Standard Model 68

[9] F.J. Hasert et al. (1974). "Observation of neutrino-like interactions without muon or electron in the Gargamelle neutrino experiment". Nuclear 

 Physics B 73: 1. doi:10.1016/0550-3213(74)90038-8.

[10] D. Haidt (4 October 2004). "The discovery of the weak neutral currents" (http://cerncourier. com/cws/article/cern/29168). CERN 

Courier . . Retrieved 2008-05-08.

[11] "Details can be worked out if the situation is simple enough for us to make an approximation, which is almost never, but often we can

understand more or less what is happening." from The Feynman Lectures on Physics, Vol 1. pp. 2 –7

[12] Technically, there are nine such color –anticolor combinations. However there is one color symmetric combination that can be constructed

out of a linear superposition of the nine combinations, reducing the count to eight.[13] F. Englert, R. Brout (1964). "Broken Symmetry and the Mass of Gauge Vector Mesons". Physical Review Letters 13: 321 –323.

doi:10.1103/PhysRevLett.13.321.

[14] P.W. Higgs (1964). "Broken Symmetries and the Masses of Gauge Bosons". Physical Review Letters 13: 508 –509.

doi:10.1103/PhysRevLett.13.508.

[15] G.S. Guralnik, C.R. Hagen, T.W.B. Kibble (1964). "Global Conservation Laws and Massless Particles". Physical Review Letters 13:

585 –587. doi:10.1103/PhysRevLett.13.585.

[16] G.S. Guralnik (2009). "The History of the Guralnik, Hagen and Kibble development of the Theory of Spontaneous Symmetry Breaking and

Gauge Particles". International Journal of Modern Physics A 24: 2601 –2627. doi:10.1142/S0217751X09045431. arXiv:0907.3466.

[17] A. Cho (23 January 2008). "Higgs Hiding in Plain Sight?" (http://sciencenow.sciencemag. org/cgi/content/full/2008/123/3).

ScienceNOW. . Retrieved 2008-05-08.

[18] The normalization Q = I 3

+ Y is sometimes used instead.

[19] W.-M. Yao et al. (Particle Data Group) (2006). "Review of Particle Physics: Quarks" (http://pdg. 

lbl. 

gov/2006/tables/qxxx. 

pdf). Journalof Physics G 33: 1. doi:10.1088/0954-3899/33/1/001. .

[20] W.-M. Yao et al. (Particle Data Group) (2006). "Review of Particle Physics: Neutrino mass, mixing, and flavor change" (http://pdg.  lbl.

gov/2007/reviews/numixrpp. pdf). Journal of Physics G 33: 1. .

[21] http://press. web. cern. ch/press/PressReleases/Releases2010/PR08.10E.html

References

Further reading

• R. Oerter (2006). The Theory of Almost Everything: The Standard Model, the Unsung Triumph of Modern

 Physics. Plume.

• B.A. Schumm (2004). Deep Down Things: The Breathtaking Beauty of Particle Physics. Johns HopkinsUniversity Press. ISBN 0-8018-7971-X.

• V. Stenger (2000). Timeless Reality. Prometheus Books. See chapters 9 –12 in particular.

Introductory textbooks

• I. Aitchison, A. Hey (2003). Gauge Theories in Particle Physics: A Practical Introduction.. Institute of Physics.

ISBN 9780585445502.

• W. Greiner, B. Müller (2000). Gauge Theory of Weak Interactions. Springer. ISBN 3-540-67672-4.

• G.D. Coughlan, J.E. Dodd, B.M. Gripaios (2006). The Ideas of Particle Physics: An Introduction for Scientists.

Cambridge University Press.

• D.J. Griffiths (1987). Introduction to Elementary Particles. John Wiley & Sons. ISBN 0-471-60386-4.

• G.L. Kane (1987). Modern Elementary Particle Physics. Perseus Books. ISBN 0-201-11749-5.

Advanced textbooks

• T.P. Cheng, L.F. Li (2006). Gauge theory of elementary particle physics. Oxford University Press.

ISBN 0-19-851961-3. Highlights the gauge theory aspects of the Standard Model.

• J.F. Donoghue, E. Golowich, B.R. Holstein (1994). Dynamics of the Standard Model. Cambridge University

Press. ISBN 978-0521476522. Highlights dynamical and phenomenological aspects of the Standard Model.

• L. O'Raifeartaigh (1988). Group structure of gauge theories. Cambridge University Press. ISBN 0-521-34785-8.

Highlights group-theoretical aspects of the Standard Model.

Journal articles

• E.S. Abers, B.W. Lee (1973). "Gauge theories". Physics Reports 9: 1 –141. doi:10.1016/0370-1573(73)90027-6.

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Standard Model 69

• Y. Hayato et al. (1999). "Search for Proton Decay through p → νK + in a Large Water Cherenkov Detector".

 Physical Review Letters 83: 1529. doi:10.1103/PhysRevLett.83.1529.

• S.F. Novaes (2000). "Standard Model: An Introduction". arΧiv:hep-ph/0001283 [hep-ph].

• D.P. Roy (1999). "Basic Constituents of Matter and their Interactions — A Progress Report.".

arΧiv:hep-ph/9912523 [hep-ph].

• F. Wilczek (2004). "The Universe Is A Strange Place". arΧiv:astro-ph/0401347 [astro-ph].

External links

• " Standard Model - explanation for beginners (http://cms. web.cern. ch/cms/Physics/StandardPackage/index.

html)" LHC 

• " Standard Model may be found incomplete, (http://www. newscientist. com/news/news.  jsp?id=ns9999404)"

 New Scientist .

• " Observation of the Top Quark (http://www-cdf. fnal.gov/top_status/top.  html)" at Fermilab.

• " The Standard Model Lagrangian. (http://cosmicvariance. com/2006/11/23/thanksgiving)" After electroweak

symmetry breaking, with no explicit Higgs boson.

• " Standard Model Lagrangian (http://nuclear.ucdavis. edu/~tgutierr/files/stmL1.  html)" with explicit Higgsterms. PDF, PostScript, and LaTeX versions.

• " The particle adventure. (http://particleadventure. org/)" Web tutorial.

• Nobes, Matthew (2002) "Introduction to the Standard Model of Particle Physics" on Kuro5hin: Part 1, (http:// 

www. kuro5hin. org/story/2002/5/1/3712/31700) Part 2, (http://www. kuro5hin. org/story/2002/5/14/ 

19363/8142) Part 3a, (http://www. kuro5hin. org/story/2002/7/15/173318/784) Part 3b. (http://www.

kuro5hin. org/story/2002/8/21/195035/576)

Particle physics

Collision of 2 beams of gold atoms recorded by RHIC

Particle physics is a branch of physics that studies the

elementary subatomic constituents of matter and

radiation, and the interactive relationship between

them. It is also called high energy physics, because

many elementary particles do not occur under normal

circumstances in nature due to energetic instability, but

can be created and detected during high energy

collisions with other particles, as is done in particle

accelerators.

Scientific research in this area has produced a long list

of particles.

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Particle physics 70

Subatomic particles

An image showing 6 quarks, 6 leptons and the interacting particles, according to

the Standard Model

Modern particle physics research is focused

on subatomic particles, including atomic

constituents such as electrons, protons, and

neutrons (protons and neutrons are actually

composite particles, made up of quarks),particles produced by radioactive and

scattering processes, such as photons,

neutrinos, and muons, as well as a wide

range of exotic particles.

Strictly speaking, the term  particle is a

misnomer because the dynamics of particle

physics are governed by quantum

mechanics. As such, they exhibit

wave-particle duality, displayingparticle-like behavior under certain

experimental conditions and wave-like

behavior in others (more technically they are

described by state vectors in a Hilbert space;

see quantum field theory). Following the

convention of particle physicists,

"elementary particles" refer to objects such

as electrons and photons, it is well known

that these "particles" display wave-like properties as well.

All the particles and their interactions observed to date can almost be described entirely by a quantum field theory

called the Standard Model. The Standard Model has 17 species of elementary particles: 12 fermions (24 if you count

antiparticles separately), 4 vector bosons (5 if you count antiparticles separately), and 1 scalar boson. These

elementary particles can combine to form composite particles, accounting for the hundreds of other species of 

particles discovered since the 1960s. The Standard Model has been found to agree with almost all the experimental

tests conducted to date. However, most particle physicists believe that it is an incomplete description of nature, and

that a more fundamental theory awaits discovery. In recent years, measurements of neutrino mass have provided the

first experimental deviations from the Standard Model.

Particle physics has had a large impact on the philosophy of science. Some particle physicists adhere to

reductionism, a point of view that has been criticized and defended by philosophers and scientists. Part of the debateis described below.[1] [2] [3] [4]

History

The idea that all matter is composed of elementary particles dates to at least the 6th century BC. The philosophical

doctrine of atomism and the nature of elementary particles were studied by ancient Greek philosophers such as

Leucippus, Democritus and Epicurus; ancient Indian philosophers such as Kanada, Dignāga and Dharmakirti;

medieval scientists such as Alhazen, Avicenna and Algazel; and early modern European physicists such as Pierre

Gassendi, Robert Boyle and Isaac Newton. The particle theory of light was also proposed by Alhazen, Avicenna,

Gassendi and Newton. These early ideas were founded in abstract, philosophical reasoning rather than

experimentation and empirical observation.

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Particle physics 71

In the 19th century, John Dalton, through his work on stoichiometry, concluded that each element of nature was

composed of a single, unique type of particle. Dalton and his contemporaries believed these were the fundamental

particles of nature and thus named them atoms, after the Greek word atomos, meaning "indivisible". However, near

the end of the century, physicists discovered that atoms were not, in fact, the fundamental particles of nature, but

conglomerates of even smaller particles. The early 20th century explorations of nuclear physics and quantum physics

culminated in proofs of nuclear fission in 1939 by Lise Meitner (based on experiments by Otto Hahn), and nuclear

fusion by Hans Bethe in the same year. These discoveries gave rise to an active industry of generating one atom from

another, even rendering possible (although not profitable) the transmutation of lead into gold. They also led to the

development of nuclear weapons. Throughout the 1950s and 1960s, a bewildering variety of particles were found in

scattering experiments. This was referred to as the "particle zoo". This term was deprecated after the formulation of 

the Standard Model during the 1970s in which the large number of particles was explained as combinations of a

(relatively) small number of fundamental particles.

The Standard Model

The current state of the classification of elementary particles is the Standard Model. It describes the strong, weak,

and electromagnetic fundamental forces, using mediating gauge bosons. The species of gauge bosons are the gluons,W− and W+ and Z bosons, and the photons. The model also contains 24 fundamental particles, which are the

constituents of matter. Finally, it predicts the existence of a type of boson known as the Higgs boson, which is yet to

be discovered.

Experimental laboratories

In particle physics, the major international laboratories are:

• Brookhaven National Laboratory (Long Island, United States). Its main facility is the Relativistic Heavy Ion

Collider (RHIC) which collides heavy ions such as gold ions and polarized protons. It is the world's first heavy

ion collider, and the world's only polarized proton collider.• Budker Institute of Nuclear Physics (Novosibirsk, Russia)

• CERN, (Franco-Swiss border, near Geneva). Its main project is now the Large Hadron Collider (LHC), which had

its first beam circulation on 10 September 2008, and is now the world's most energetic collider of protons. It will

also be the most energetic collider of heavy ions when it begins colliding lead ions in 2010. Earlier facilities

include the Large Electron –Positron Collider (LEP), which was stopped in 2001 and then dismantled to give way

for LHC; and the Super Proton Synchrotron, which is being reused as a pre-accelerator for LHC.

• DESY (Hamburg, Germany). Its main facility is the Hadron Elektron Ring Anlage (HERA), which collides

electrons and positrons with protons.

• Fermilab, (Batavia, United States). Its main facility is the Tevatron, which collides protons and antiprotons and

was the highest energy particle collider in the world until the Large Hadron Collider surpassed it on 29 November2009.

• KEK, (Tsukuba, Japan). It is the home of a number of experiments such as K2K, a neutrino oscillation experiment

and Belle, an experiment measuring the CP violation of B mesons.

• SLAC National Accelerator Laboratory (Menlo Park, United States). Its main facility is PEP-II, which collides

electrons and positrons.

Many other particle accelerators exist.

The techniques required to do modern experimental particle physics are quite varied and complex, constituting a

sub-specialty nearly completely distinct from the theoretical side of the field. See Category:Experimental particle

physics for a partial list of the ideas required for such experiments.

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Particle physics 72

Theory

Theoretical particle physics attempts to develop the models, theoretical framework, and mathematical tools to

understand current experiments and make predictions for future experiments. See also theoretical physics. There are

several major interrelated efforts in theoretical particle physics today. One important branch attempts to better

understand the standard model and its tests. By extracting the parameters of the Standard Model from experiments

with less uncertainty, this work probes the limits of the Standard Model and therefore expands our understanding of nature's building blocks. These efforts are made challenging by the difficulty of calculating quantities in quantum

chromodynamics. Some theorists working in this area refer to themselves as phenomenologists and may use the

tools of quantum field theory and effective field theory. Others make use of lattice field theory and call themselves

lattice theorists.

Another major effort is in model building where model builders develop ideas for what physics may lie beyond the

Standard Model (at higher energies or smaller distances). This work is often motivated by the hierarchy problem and

is constrained by existing experimental data. It may involve work on supersymmetry, alternatives to the Higgs

mechanism, extra spatial dimensions (such as the Randall-Sundrum models), Preon theory, combinations of these, or

other ideas.

A third major effort in theoretical particle physics is string theory. String theorists attempt to construct a unified

description of quantum mechanics and general relativity by building a theory based on small strings, and branes

rather than particles. If the theory is successful, it may be considered a "Theory of Everything".

There are also other areas of work in theoretical particle physics ranging from particle cosmology to loop quantum

gravity.

This division of efforts in particle physics is reflected in the names of categories on the preprint archive [5]: hep-th

(theory), hep-ph (phenomenology), hep-ex (experiments), hep-lat (lattice gauge theory).

The future

Particle physicists internationally agree on the most important goals of particle physics research in the near and

intermediate future. The overarching goal, which is pursued in several distinct ways, is to find and understand what

physics may lie beyond the standard model. There are several powerful experimental reasons to expect new physics,

including dark matter and neutrino mass. There are also theoretical hints that this new physics should be found at

accessible energy scales. Most importantly, though, there may be unexpected and unpredicted surprises which will

give us the most opportunity to learn about nature.

Much of the efforts to find this new physics are focused on new collider experiments. A (relatively) near term goal is

the completion of the Large Hadron Collider (LHC) in 2008 which will continue the search for the Higgs boson,

supersymmetric particles, and other new physics. An intermediate goal is the construction of the International Linear

Collider (ILC) which will complement the LHC by allowing more precise measurements of the properties of newlyfound particles. A decision for the technology of the ILC has been taken in August 2004, but the site has still to be

agreed upon.

Additionally, there are important non-collider experiments which also attempt to find and understand physics beyond

the Standard Model. One important non-collider effort is the determination of the neutrino masses since these masses

may arise from neutrinos mixing with very heavy particles. In addition, cosmological observations provide many

useful constraints on the dark matter, although it may be impossible to determine the exact nature of the dark matter

without the colliders. Finally, lower bounds on the very long lifetime of the proton put constraints on Grand

Unification Theories at energy scales much higher than collider experiments will be able to probe any time soon.

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Particle physics 73

See also

• Atomic physics

• Beyond the Standard Model

• Elementary particle

• High pressure physics

• Interactions:• Strong

• Weak

• Introduction to quantum mechanics

• List of accelerators in particle physics

• List of particles:

• Baryon

• Boson

• Fermion

• Hadron

• Lepton

• Meson

• Quark

• Magnetic Monopole

• Micro black hole

• Resonance (particle physics)

• Rochester conference

• Standard model (mathematical formulation)

• Stanford Physics Information Retrieval System

• Subatomic particle• Timeline of particle physics

• Unparticle physics

References

[1] "Review of particle physics" (http://pdg.lbl. gov/). .

[2] "Particle Physics News and Resources" (http://www. interactions.org/). .

[3] "CERN Courier - International Journal of High-Energy Physics" (http://cerncourier.  com). .

[4] "Particle physics in 60 seconds" (http://www. symmetrymagazine.org/cms/?pid=1000345). .

[5] http://www. arxiv. org

Further reading

General readers

• Frank Close (2004) Particle Physics: A Very Short Introduction. Oxford University Press. ISBN 0-19-280434-0.

• --------, Michael Marten, and Christine Sutton (2002) The Particle Odyssey: A Journey to the Heart of the Matter .

Oxford Univ. Press. ISBN 0-19-850486-1.

• Ford, Kenneth W. (2005) The Quantum World . Harvard Univ. Press.

• Oerter, Robert (2006) The Theory of Almost Everything: The Standard Model, the Unsung Triumph of Modern

 Physics. Plume.

• Schumm, Bruce A. (2004) Deep Down Things: The Breathtaking Beauty of Particle Physics. John Hopkins Univ.Press. ISBN 0-8018-7971-X.

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Particle physics 74

Gentle texts

• Frank Close (2006) The New Cosmic Onion. Taylor & Francis. ISBN 1-58488-798-2.

• Coughlan, G. D., J. E. Dodd, and B. M. Gripaios (2006) The Ideas of Particle Physics: An Introduction for 

Scientists, 3rd ed. Cambridge Univ. Press. An undergraduate text for those not majoring in physics.

HarderA survey article:

• Robinson, Matthew B., Karen R. Bland, Gerald Cleaver, and J. R. Dittmann (2008) "A Simple Introduction to

Particle Physics" - Part 1, 135pp. (http://arxiv. org/abs/0810.  3328v1) and Part 2, nnnpp. (http://arxiv.  org/ 

abs/0908.  1395v1) Baylor University Dept. of Physics.

Texts:

• Griffiths, David J. (1987). Introduction to Elementary Particles. Wiley, John & Sons, Inc. ISBN 0-471-60386-4.

• Kane, Gordon L. (1987). Modern Elementary Particle Physics. Perseus Books. ISBN 0-201-11749-5.

• Perkins, Donald H. (1999). Introduction to High Energy Physics. Cambridge University Press.

ISBN 0-521-62196-8.• Povh, Bogdan (1995). Particles and Nuclei: An Introduction to the Physical Concepts. Springer-Verlag.

ISBN 0-387-59439-6.

External links

• The Particle Adventure (http://particleadventure. org/) - educational project sponsored by the Particle Data

Group of the Lawrence Berkeley National Laboratory (LBNL)

• symmetry magazine (http://www. symmetrymagazine. org)

• Nobes, Matthew (2002) "Introduction to the Standard Model of Particle Physics" on Kuro5hin: Part 1, (http:// 

www. kuro5hin. org/story/2002/5/1/3712/31700) Part 2, (http://www. kuro5hin. org/story/2002/5/14/ 

19363/8142) Part 3a, (http://www. kuro5hin. org/story/2002/7/15/173318/784) Part 3b. (http://www.

kuro5hin. org/story/2002/8/21/195035/576)

• CERN (http://public. web.cern. ch/public/) - European Organization for Nuclear Research

• Fermilab (http://www. fnal. gov/)

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Superpartner 75

Superpartner

In particle physics, a superpartner (also sparticle) is a hypothetical elementary particle. Supersymmetry is one of 

the synergistic bleeding-edge theories in current high-energy physics which predicts the existence of these "shadow"

particles.

The word superpartner  is a portmanteau of the words supersymmetry and  partner  (sparticle is a portmanteau of 

supersymmetry and particle).

Theoretical predictions

According to the supersymmetry theory, each fermion should have a partner boson, the fermion's superpartner and

each boson should have a partner fermion. When the more familiar leptons, photons, and quarks were produced in

the Big Bang, each one was accompanied by a matching sparticle: sleptons, photinos and squarks. This state of 

affairs occurred at a time when the universe was undergoing a rapid phase change, and theorists believe this state of 

affairs lasted only some ten trillionth of a ten trillionth of a nanosecond (10 −35 seconds) before the particles we see

now "condensed" out and froze into space-time. Sparticles have not existed naturally since that time.Exact unbroken supersymmetry would predict that a particle and its superpartners would have the same mass. No

superpartners of the Standard Model particles have yet been found. This may indicate that supersymmetry is

incorrect, or it may also be the result of the fact that supersymmetry is not an exact, unbroken symmetry of nature. If 

a superpartner is found, its mass would determine the scale at which supersymmetry is broken.

For particles that are real scalars (such as an axion), there is a fermion superpartner as well as a second, real scalar

field. For axions, these particles are often referred to as axinos and saxions.

In extended supersymmetry there may be more than one superparticle for a given particle. For instance, with two

copies of supersymmetry in four dimensions, a photon would have two fermion superpartners and a scalar

superpartner.In zero dimensions (often known as matrix mechanics), it is possible to have supersymmetry, but no superpartners.

However, this is the only situation where supersymmetry does not imply the existence of superpartners.

Recreating superpartners

If the supersymmetry theory is correct, it should be possible to recreate these particles in high-energy particle

accelerators. Doing so will not be an easy task; these particles may have masses up to a thousand times greater than

their corresponding "real" particles.

Until recently, colliders did not have the power to create these supermassive particles, but the newly built Large

Hadron Collider at CERN in Switzerland and France will be able to achieve collisions in the 14 TeV(tera-electron-volt) range, which is more than adequate to determine if these superpartner particles exist.

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Superpartner 76

See also

• Chargino

• Gluino

• Gravitino as a superpartner of the hypothetical graviton

• Neutralino

• Sfermion

External links

• Argonne National Laboratory [1]

• Large Hadron Collider [2]

• CERN homepage [3]

References

[1] http://www. anl. gov/OPA/Frontiers2000/b5excell.html

[2] https://edms. 

cern. 

ch/cedar/plsql/cedarw.site_home[3] http://public. web. cern. ch/public/ 

Supersymmetry

In particle physics, supersymmetry (often abbreviated SUSY) is a symmetry that relates elementary particles of one

spin to other particles that differ by half a unit of spin and are known as superpartners. In a theory with unbroken

supersymmetry, for every type of boson there exists a corresponding type of fermion with the same mass and internal

quantum numbers, and vice-versa.

So far, there is only indirect evidence for the existence of supersymmetry.[1]

Since the superpartners of the StandardModel particles have not been observed, supersymmetry, if it exists, must be a broken symmetry, allowing the

superparticles to be heavier than the corresponding Standard Model particles.

If supersymmetry exists close to the TeV energy scale, it allows for a solution of the hierarchy problem of the

Standard Model, i.e., the fact that the Higgs boson mass is subject to quantum corrections which  — barring

extremely fine-tuned cancellations among independent contributions — would make it so large as to undermine the

internal consistency of the theory. In supersymmetric theories, on the other hand, the contributions to the quantum

corrections coming from Standard Model particles are naturally canceled by the contributions of the corresponding

superpartners. Other attractive features of TeV-scale supersymmetry are the fact that it allows for the high-energy

unification of the weak interactions, the strong interactions and electromagnetism, and the fact that it provides a

candidate for Dark Matter and a natural mechanism for electroweak symmetry breaking.Another advantage of supersymmetry is that supersymmetric quantum field theory can sometimes be solved.

Supersymmetry is also a feature of most versions of string theory, though it can exist in nature even if string theory

is incorrect.

The Minimal Supersymmetric Standard Model is one of the best studied candidates for physics beyond the Standard

Model. Theories of gravity that are also invariant under supersymmetry are known as supergravity theories.

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Supersymmetry 77

History

A supersymmetry relating mesons and baryons was first proposed, in the context of hadronic physics, by Hironari

Miyazawa in 1966, but his work was ignored at the time.[2] [3] [4] [5] In the early 1970s, J. L. Gervais and B. Sakita

(in 1971), Yu. A. Golfand and E.P. Likhtman (also in 1971), D.V. Volkov and V.P. Akulov (in 1972) and J. Wess

and B. Zumino (in 1974) independently rediscovered supersymmetry, a radically new type of symmetry of spacetime

and fundamental fields, which establishes a relationship between elementary particles of different quantum nature,bosons and fermions, and unifies spacetime and internal symmetries of the microscopic world. Supersymmetry first

arose in the context of an early version of string theory by Pierre Ramond, John H. Schwarz and Andre Neveu, but

the mathematical structure of supersymmetry has subsequently been applied successfully to other areas of physics;

firstly by Wess, Zumino, and Abdus Salam and their fellow researchers to particle physics, and later to a variety of 

fields, ranging from quantum mechanics to statistical physics. It remains a vital part of many proposed theories of 

physics.

The first realistic supersymmetric version of the Standard Model was proposed in 1981 by Howard Georgi and Savas

Dimopoulos and is called the Minimal Supersymmetric Standard Model or MSSM for short. It was proposed to solve

the hierarchy problem and predicts superpartners with masses between 100 GeV and 1 TeV. As of 2009 there is no

irrefutable experimental evidence that supersymmetry is a symmetry of nature. In 2010 the Large Hadron Collider at

CERN is scheduled to produce the world's highest energy collisions and offers the best chance at discovering

superparticles for the foreseeable future. Recently prediction markets like intrade offered scientific contracts that

give estimates for that probability.

Applications

Extension of possible symmetry groups

One reason that physicists explored supersymmetry is because it offers an extension to the more familiar symmetries

of quantum field theory. These symmetries are grouped into the Poincaré group and internal symmetries and theColeman –Mandula theorem showed that under certain assumptions, the symmetries of the S-matrix must be a direct

product of the Poincaré group with a compact internal symmetry group or if there is no mass gap, the conformal

group with a compact internal symmetry group. In 1971 Golfand and Likhtman were the first to show that the

Poincaré algebra can be extended through introduction of four anticommuting spinor generators (in four

dimensions), which later became known as supercharges. In 1975 the Haag-Lopuszanski-Sohnius theorem analyzed

all possible superalgebras in the general form, including those with an extended number of the supergenerators and

central charges. This extended super-Poincaré algebra paved the way for obtaining a very large and important class

of supersymmetric field theories.

The supersymmetry algebraTraditional symmetries in physics are generated by objects that transform under the tensor representations of the

Poincaré group and internal symmetries. Supersymmetries, on the other hand, are generated by objects that transform

under the spinor representations. According to the spin-statistics theorem, bosonic fields commute while fermionic

fields anticommute. Combining the two kinds of fields into a single algebra requires the introduction of a Z2-grading

under which the bosons are the even elements and the fermions are the odd elements. Such an algebra is called a Lie

superalgebra.

The simplest supersymmetric extension of the Poincaré algebra, expressed in terms of two Weyl spinors, has the

following anti-commutation relation:

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Supersymmetry 78

and all other anti-commutation relations between the Qs and commutation relations between the Qs and Ps vanish. In

the above expression are the generators of translation and are the Pauli matrices.

There are representations of a Lie superalgebra that are analogous to representations of a Lie algebra. Each Lie

algebra has an associated Lie group and a Lie superalgebra can sometimes be extended into representations of a Lie

supergroup.

The Supersymmetric Standard Model

Incorporating supersymmetry into the Standard Model requires doubling the number of particles since there is no

way that any of the particles in the Standard Model can be superpartners of each other. With the addition of new

particles, there are many possible new interactions. The simplest possible supersymmetric model consistent with the

Standard Model is the Minimal Supersymmetric Standard Model (MSSM) which can include the necessary

additional new particles that are able to be superpartners of those in the Standard Model.

Cancellation of the Higgs boson quadratic mass renormalization between fermionic

top quark loop and scalar stop squark tadpole Feynman diagrams in a

supersymmetric extension of the Standard Model

One of the main motivations for SUSY

comes from the quadratically divergent

contributions to the Higgs mass squared.

The quantum mechanical interactions of the

Higgs boson causes a large renormalization

of the Higgs mass and unless there is an

accidental cancellation, the natural size of 

the Higgs mass is the highest scale possible.

This problem is known as the hierarchy

problem. Supersymmetry reduces the size of 

the quantum corrections by having

automatic cancellations between fermionic

and bosonic Higgs interactions. If 

supersymmetry is restored at the weak scale,

then the Higgs mass is related to

supersymmetry breaking which can be

induced from small non-perturbative effects

explaining the vastly different scales in the

weak interactions and gravitational interactions.

In many supersymmetric Standard Models there is a heavy stable particle (such as neutralino) which could serve as a

Weakly interacting massive particle (WIMP) dark matter candidate. The existence of a supersymmetric dark matter

candidate is closely tied to R-parity.

The standard paradigm for incorporating supersymmetry into a realistic theory is to have the underlying dynamics of 

the theory be supersymmetric, but the ground state of the theory does not respect the symmetry and supersymmetry

is broken spontaneously. The supersymmetry break can not be done permanently by the particles of the MSSM as

they currently appear. This means that there is a new sector of the theory that is responsible for the breaking. The

only constraint on this new sector is that it must break supersymmetry permanently and must give superparticles TeV

scale masses. There are many models that can do this and most of their details do not currently matter. In order to

parameterize the relevant features of supersymmetry breaking, arbitrary soft SUSY breaking terms are added to the

theory which temporarily break SUSY explicitly but could never arise from a complete theory of supersymmetry

breaking.

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Supersymmetry 79

Gauge Coupling Unification

One piece of evidence for supersymmetry existing is gauge coupling unification. The renormalization group

evolution of the three gauge coupling constants of the Standard Model is somewhat sensitive to the present particle

content of the theory. These coupling constants do not quite meet together at a common energy scale if we run the

renormalization group using the Standard Model.[1] With the addition of minimal SUSY joint convergence of the

coupling constants is projected at approximately 1016

GeV.[1]

Supersymmetric quantum mechanics

Supersymmetric quantum mechanics adds the SUSY superalgebra to quantum mechanics as opposed to quantum

field theory. Supersymmetric quantum mechanics often comes up when studying the dynamics of supersymmetric

solitons and due to the simplified nature of having fields only functions of time (rather than space-time), a great deal

of progress has been made in this subject and is now studied in its own right.

SUSY quantum mechanics involves pairs of Hamiltonians which share a particular mathematical relationship, which

are called   partner Hamiltonians. (The potential energy terms which occur in the Hamiltonians are then called

  partner potentials.) An introductory theorem shows that for every eigenstate of one Hamiltonian, its partner

Hamiltonian has a corresponding eigenstate with the same energy. This fact can be exploited to deduce many

properties of the eigenstate spectrum. It is analogous to the original description of SUSY, which referred to bosons

and fermions. We can imagine a "bosonic Hamiltonian", whose eigenstates are the various bosons of our theory. The

SUSY partner of this Hamiltonian would be "fermionic", and its eigenstates would be the theory's fermions. Each

boson would have a fermionic partner of equal energy.

SUSY concepts have provided useful extensions to the WKB approximation. In addition, SUSY has been applied to

non-quantum statistical mechanics through the Fokker-Planck equation.

Mathematics

SUSY is also sometimes studied mathematically for its intrinsic properties. This is because it describes complexfields satisfying a property known as holomorphy, which allows holomorphic quantities to be exactly computed.

This makes supersymmetric models useful toy models of more realistic theories. A prime example of this has been

the demonstration of S-duality in four-dimensional gauge theories that interchanges particles and monopoles.

General supersymmetry

Supersymmetry appears in many different contexts in theoretical physics that are closely related. It is possible to

have multiple supersymmetries and also have supersymmetric extra dimensions.

Extended supersymmetry

It is possible to have more than one kind of supersymmetry transformation. Theories with more than one

supersymmetry transformation are known as extended supersymmetric theories. The more supersymmetry a theory

has, the more constrained the field content and interactions are. Typically the number of copies of a supersymmetry

is a power of 2, i.e. 1, 2, 4, 8. In four dimensions, a spinor has four degrees of freedom and thus the minimal number

of supersymmetry generators is four in four dimensions and having eight copies of supersymmetry means that there

are 32 supersymmetry generators.

The maximal number of supersymmetry generators possible is 32. Theories with more than 32 supersymmetry

generators automatically have massless fields with spin greater than 2. It is not known how to make massless fields

with spin greater than two interact, so the maximal number of supersymmetry generators considered is 32. This

corresponds to an N = 8 supersymmetry theory. Theories with 32 supersymmetries automatically have a graviton.

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Supersymmetry 80

In four dimensions there are the following theories, with the corresponding multiplets [6] (CPT adds a copy,

whenever they are not invariant under such symmetry)

•  N = 1

Chiral multiplet: (0,1 ⁄ 2) Vector multiplet: (1 ⁄ 

2,1) Gravitino multiplet: (1,3 ⁄ 

2) Graviton multiplet: (3 ⁄ 

2,2)

•  N = 2

hypermultiplet: (-1 ⁄ 2,02,1 ⁄ 

2) vector multiplet: (0,1 ⁄ 

22,1) supergravity multiplet: (1,3 ⁄ 

22,2)

•  N = 4

Vector multiplet: (-1,-1 ⁄ 24,06,1 ⁄ 

24,1) Supergravity multiplet: (0,1 ⁄ 

24,16,3 ⁄ 

24,2)

•  N = 8

Supergravity multiplet: (-2,-3 ⁄ 28,-128,-1 ⁄ 

256,070,1 ⁄ 

256,128,3 ⁄ 

28,2)

Supersymmetry in alternate numbers of dimensions

It is possible to have supersymmetry in dimensions other than four. Because the properties of spinors change

drastically between different dimensions, each dimension has its characteristic. In d dimensions, the size of spinors is

roughly 2d  /2 or 2(d  − 1)/2. Since the maximum number of supersymmetries is 32, the greatest number of dimensions in

which a supersymmetric theory can exist is eleven.

Supersymmetry as a quantum group

Supersymmetry can be reinterpreted in the language of noncommutative geometry and quantum groups. In

particular, it involves a mild form of noncommutativity, namely supercommutativity. See the main article for more

details.

Supersymmetry in quantum gravity

Supersymmetry is part of a larger enterprise of theoretical physics to unify everything we know about the physical

world into a single fundamental framework of physical laws, known as the quest for a Theory of Everything (TOE).

A significant part of this larger enterprise is the quest for a theory of quantum gravity, which would unify the

classical theory of general relativity and the Standard Model, which explains the other three basic forces in physics

(electromagnetism, the strong interaction, and the weak interaction), and provides a palette of fundamental particles

upon which all four forces act. Two of the most active approaches to forming a theory of quantum gravity are string

theory and loop quantum gravity (LQG), although in theory, supersymmetry could be a component of other

theoretical approaches as well.

For string theory to be consistent, supersymmetry appears to be required at some level (although it may be a strongly

broken symmetry). In particle theory, supersymmetry is recognized as a way to stabilize the hierarchy between theunification scale and the electroweak scale (or the Higgs boson mass), and can also provide a natural dark matter

candidate. String theory also requires extra spatial dimensions which have to be compactified as in Kaluza-Klein

theory.

Loop quantum gravity (LQG), in its current formulation, predicts no additional spatial dimensions, nor anything else

about particle physics. These theories can be formulated in three spatial dimensions and one dimension of time,

although in some LQG theories dimensionality is an emergent property of the theory, rather than a fundamental

assumption of the theory. Also, LQG is a theory of quantum gravity which does not require supersymmetry. Lee

Smolin, one of the originators of LQG, has proposed that a loop quantum gravity theory incorporating either

supersymmetry or extra dimensions, or both, be called "loop quantum gravity II".

If experimental evidence confirms supersymmetry in the form of supersymmetric particles such as the neutralino that

is often believed to be the lightest superpartner, some people believe this would be a major boost to string theory.

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Supersymmetry 81

Since supersymmetry is a required component of string theory, any discovered supersymmetry would be consistent

with string theory. If the Large Hadron Collider and other major particle physics experiments fail to detect

supersymmetric partners or evidence of extra dimensions, many versions of string theory which had predicted certain

low mass superpartners to existing particles may need to be significantly revised. The failure of experiments to

discover either supersymmetric partners or extra spatial dimensions, as of 2009, has encouraged loop quantum

gravity researchers.

See also

• Concise Encyclopedia of Supersymmetry (book)

• Minimal Supersymmetric Standard Model

• Quantum group

• Supergravity

• Supergeometry

• Supergroup

• Superspace

• Supercharge

References

[1] Gordon L. Kane, The Dawn of Physics Beyond the Standard Model, Scientific American, June 2003, page 60 and The frontiers of physics,

special edition, Vol 15, #3, page 8 "Indirect evidence for supersymmetry comes from the extrapolation of interactions to high energies."

[2] H. Miyazawa (1966). "Baryon Number Changing Currents". Prog. Theor. Phys. 36 (6): 1266 –1276. doi:10.1143/PTP.36.1266.

[3] H. Miyazawa (1968). "Spinor Currents and Symmetries of Baryons and Mesons". Phys. Rev. 170 (5): 1586 –1590.

doi:10.1103/PhysRev.170.1586.

[4] Michio Kaku, Quantum Field Theory, ISBN 0-19-509158-2, pg 663.

[5] Peter Freund, Introduction to Supersymmetry , ISBN 0-521-35675-X, pages 26-27, 138.

[6] Polchinski,J. String theory. Vol. 2: Superstring theory and beyond , Appendix B

Further reading

• Miyazawa Supersymmetry (http://nucl.phys. s.u-tokyo.  ac.  jp/kimiko/fm50/catto.  pdf) by Sultan Catto, 2008

• A Supersymmetry Primer (http://arxiv. org/pdf/hep-ph/9709356) by S. Martin, 1999

• Introduction to Supersymmetry (http://arxiv. org/pdf/hep-th/9612114) By Joseph D. Lykken, 1996

• An Introduction to Supersymmetry (http://arxiv. org/pdf/hep-ph/9611409) By Manuel Drees, 1996

• Introduction to Supersymmetry (http://arxiv. org/pdf/hep-th/0101055) By Adel Bilal, 2001

• An Introduction to Global Supersymmetry (http://www. physics. uc.edu/~argyres/661/susy2001.  pdf) by

Philip Arygres, 2001

• Weak Scale Supersymmetry (http://www.cambridge.org/uk/catalogue/catalogue. 

asp?isbn=0521857864) byHoward Baer and Xerxes Tata, 2006.

• Cooper, F., A. Khare and U. Sukhatme. "Supersymmetry in Quantum Mechanics." Phys. Rep. 251 (1995) 267-85

(arXiv:hep-th/9405029).

• Junker, G. Supersymmetric Methods in Quantum and Statistical Physics, Springer-Verlag (1996).

• Gordon L. Kane.Supersymmetry: Unveiling the Ultimate Laws of Nature Basic Books, New York (2001). ISBN

0-7382-0489-7.

• Gordon L. Kane and Shifman, M., eds. The Supersymmetric World: The Beginnings of the Theory, World

Scientific, Singapore (2000). ISBN 981-02-4522-X.

• D.V. Volkov, V.P. Akulov, Pisma Zh.Eksp.Teor.Fiz. 16 (1972) 621; Phys.Lett. B46 (1973) 109.

• V.P. Akulov, D.V. Volkov, Teor.Mat.Fiz. 18 (1974) 39.

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Supersymmetry 82

• Weinberg, Steven, The Quantum Theory of Fields, Volume 3: Supersymmetry, Cambridge University Press,

Cambridge, (1999). ISBN 0-521-66000-9.

• Wess, Julius, and Jonathan Bagger, Supersymmetry and Supergravity, Princeton University Press, Princeton,

(1992). ISBN 0-691-02530-4.

• Bennett GW, et al.; Muon (g−2) Collaboration (2004). "Measurement of the negative muon anomalous magnetic

moment to 0.7 ppm". Physical Review Letters 92 (16): 161802. doi:10.1103/PhysRevLett.92.161802.

PMID 15169217.

• Brookhaven National Laboratory (Jan. 8, 2004). New g− 2 measurement deviates further from Standard Model

(http://www.  bnl. gov/bnlweb/pubaf/pr/2004/bnlpr010804.  htm). Press Release.

• Fermi National Accelerator Laboratory (Sept 25, 2006). Fermilab's CDF scientists have discovered the

quick-change behavior of the B-sub-s meson. (http://www.fnal.  gov/pub/presspass/press_releases/ 

CDF_meson. html) Press Release.

External links

• "Particle wobble shakes up supersymmetry" (http://www. cosmosmagazine.com/node/714), Cosmos magazine,

September 2006

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Higgs boson 83

Higgs boson

 Higgs boson

A simulated event, featuring the appearance of the Higgs boson

Composition: Elementary particle

Particle statistics: Bosonic

Status: Hypothetical

Theorized: F. Englert, R. Brout, P. Higgs, G. S. Guralnik, C. R. Hagen, and T. W. B. Kibble 1964

Mass: between 115 and 185 GeV/c2 (predicted)

Spin: 0

The Higgs boson is a hypothetical massive scalar elementary particle predicted to exist by the Standard Model of 

particle physics. At present there are no known elementary scalar bosons (spin-0 particles) in nature, although many

composite spin-0 particles are known. The existence of the particle is postulated as a means of resolving

inconsistencies in current theoretical physics, and attempts are being made to confirm the existence of the particle byexperimentation, using the Large Hadron Collider (LHC) at CERN and the Tevatron at Fermilab. Other theories

exist that do not anticipate the Higgs boson, described elsewhere as the Higgsless model.

The Higgs boson is the only Standard Model particle that has not been observed and is thought to be the mediator of 

mass. Experimental detection of the Higgs boson would help explain the origin of mass in the universe. The Higgs

boson would explain the difference between the massless photon, which mediates electromagnetism, and the massive

W and Z bosons, which mediate the weak force. If the Higgs boson exists, it is an integral and pervasive component

of the material world.

Arguments based on the Standard Model suggest the mass of the Higgs is below 1.4 TeV. Therefore the Large

Hadron Collider

[1]

is expected to provide experimental evidence of the existence or non-existence of the Higgsboson. Experiments at Fermilab also continue previous attempts at detection, albeit hindered by the lower energy of 

the Tevatron accelerator, although it theoretically has the necessary energy to produce the Higgs boson. It has been

reported that Fermilab physicists suggest that the odds of the Tevatron detecting the Higgs boson, if indeed it exists,

are between 50% and 96%, depending on its mass.[2]

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Higgs boson 84

Origin of the theory

2010 APS J.J. Sakurai Prize Winners

The Higgs mechanism (or

"Englert-Brout-Higgs-Guralnik-Hagen-Kibble" [3] ) which gives mass

to vector bosons, was theorized in 1964 by François Englert and

Robert Brout ("boson scalaire");[4] in October of the same year by

Peter Higgs,[5] working from the ideas of Philip Anderson; andindependently by Gerald Guralnik, C. R. Hagen, and Tom Kibble,[6]

who worked out the results by the spring of 1963.[7]

The three papers written on this discovery by Guralnik, Hagen, Kibble,

Higgs, Brout, and Englert were each recognized as milestone papers

during  Physical Review Letters 50th anniversary celebration.[8] While

each of these famous papers took similar approaches, the contributions and differences between the 1964 PRL

Symmetry Breaking papers is noteworthy. These six physicists were also awarded the 2010 J. J. Sakurai Prize for

Theoretical Particle Physics for this work.[9]

Steven Weinberg and Abdus Salam were the first to apply the Higgs mechanism to the electroweak symmetrybreaking. The electroweak theory predicts a neutral particle whose mass is not far from that of the W and Z bosons.

Theoretical overview

A one-loop Feynman diagram of the first-order

correction to the Higgs mass. The Higgs boson couples

strongly to the top quark so it may decay into top

anti-top quark pairs.

The Higgs boson particle is one quantum component of the

theoretical Higgs field. In empty space, the Higgs field has an

amplitude different from zero; i.e., a non-zero vacuum expectation

value. The existence of this non-zero vacuum expectation plays a

fundamental role: it gives mass to every elementary particle that

couples to the Higgs field, including the Higgs boson itself. Inparticular, the acquisition of a non-zero vacuum expectation value

spontaneously breaks electroweak gauge symmetry, which

scientists often refer to as the Higgs mechanism. This is the

simplest mechanism capable of giving mass to the gauge bosons

while remaining compatible with gauge theories. In essence, this

field is analogous to a pool of molasses that "sticks" to the otherwise massless fundamental particles that travel

through the field, converting them into particles with mass that form, for example, the components of atoms. Prof.

David J. Miller of University College London provided a simple explanation of the Higgs Boson, for which he won

an award.[10]

In the Standard Model, the Higgs field consists of two neutral and two charged component fields. Both of the

charged components and one of the neutral fields are Goldstone bosons, which act as the longitudinal

third-polarization components of the massive W+, W –, and Z bosons. The quantum of the remaining neutral

component corresponds to the massive Higgs boson. Since the Higgs field is a scalar field, the Higgs boson has no

spin, hence no intrinsic angular momentum. The Higgs boson is also its own antiparticle and is CP-even.

The Standard Model does not predict the mass of the Higgs boson. If that mass is between 115 and 180 GeV/c2, then

the Standard Model can be valid at energy scales all the way up to the Planck scale (1016 TeV). Many theorists

expect new physics beyond the Standard Model to emerge at the TeV-scale, based on unsatisfactory properties of the

Standard Model. The highest possible mass scale allowed for the Higgs boson (or some other electroweak symmetry

breaking mechanism) is 1.4 TeV; beyond this point, the Standard Model becomes inconsistent without such amechanism, because unitarity is violated in certain scattering processes. Many models of supersymmetry predict that

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Higgs boson 85

the lightest Higgs boson (of several) will have a mass only slightly above the current experimental limits, at around

120 GeV or less.

Supersymmetric extensions of the Standard Model (so called SUSY) predict the existence of whole families of Higgs

bosons, as opposed to a single Higgs particle of the Standard Model. Among the SUSY models, in the Minimal

Supersymmetric extension (MSSM) the Higgs mechanism yields the smallest number of Higgs bosons: there are two

Higgs doublets, leading to the existence of a quintet of scalar particles: two CP-even neutral Higgs bosons h and H, aCP-odd neutral Higgs boson A, and two charged Higgs particles H±.

There are over a hundred theoretical Higgs-mass predictions.[11]

Experimental search

Status as of August 2010, to 95% confidence interval

A Feynman diagram of one way the Higgs boson may

be produced at the LHC. Here, two gluons decay into a

top/anti-top pair, which then combine to make a neutral

Higgs.

As of August 2010, the Higgs boson

has yet to be confirmed

experimentally,[12] despite large efforts

invested in accelerator experiments at

CERN and Fermilab.Prior to the year 2000, the data

gathered at the LEP collider at CERN

allowed an experimental lower bound

to be set for the mass of the Standard

Model Higgs boson of 114.4 GeV/ c2 at

95% confidence level. The same

experiment has produced a small

number of events that could be

interpreted as resulting from Higgs

bosons with mass just above saidcutoff  —around 115 GeV —but the

number of events was insufficient to

draw definite conclusions.[13] The LEP

was shut down in 2000 due to

construction of its successor, the Large

Hadron Collider which is expected to

be able to confirm or reject the

existence of the Higgs boson. Full

operational mode was delayed until mid-November 2009, because of a serious fault discovered with a number of 

magnets during the calibration and startup phase.[14] [15]

At the Fermilab Tevatron, there are ongoing experiments searching for the Higgs boson. As of July 2010, combined

data from CDF and DØ experiments at the Tevatron were

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Higgs boson 86

A Feynman diagram of another way the Higgs boson

may be produced at the LHC. Here, two quarks each

emit a W or Z boson, which combine to make a neutral

Higgs.

sufficient to exclude the Higgs boson in the range between

158 GeV/ c2 and 175 GeV/ c2 at the 95% confidence level.[16]  [17]

Data collection and analysis in search of Higgs are intensifying

since March 30, 2010 when the LHC began operating at 3.5 Tev

and is rapidly approaching in its design range of 7 Tev, well above

that at which detection should occur.[18]

It may be possible to estimate the mass of the Higgs boson indirectly. In the Standard Model, the Higgs boson has a

number of indirect effects; most notably, Higgs loops result in tiny corrections to masses of W and Z bosons.Precision measurements of electroweak parameters, such as the Fermi constant and masses of W/Z bosons, can be

used to constrain the mass of the Higgs. As of 2006, measurements of electroweak observables allowed the exclusion

of a Standard Model Higgs boson having a mass greater than 285 GeV/ c2 at 95% CL, and estimated its mass to be

129 GeV/ c2 (the central value corresponds to approximately 138 proton masses). [19] As of August 2009, the

Standard Model Higgs boson is excluded by electroweak measurements above 186 GeV at 95% CL. However, it

should be noted that these indirect constraints make the assumption that the Standard Model is correct. One may still

discover a Higgs boson above 186 GeV if it is accompanied by other particles between Standard Model and GUT

scales.

Some have argued that there already exists potential evidence,[20] [21] [22] but to date no such evidence has convinced

the physics community.In a 2009 preprint,[23] it has been suggested (and reported under headlines such as   Higgs could reveal itself in

 Dark-Matter collisions[24] ) that the Higgs Boson might not only interact with the above-mentioned particles of the

Standard model of particle physics, but also with the mysterious WIMPs ("weakly interacting massive particles") of 

the Dark matter, playing a most-important role in recent astrophysics. In this case, it is natural to augment the above

Feynman diagrams by terms representing such an interaction.

In principle, a relation between the Higgs particle and the Dark matter would be "not unexpected", since, (i), the

Higgs field does not directly couple to the quanta of light (i.e. the photons), while at the same time, (ii), it generates

mass. However, "dark matter" is a metonymy for the discrepancy between the apparent observed mass of the

universe and that given by the standard model and is not a component of any known theory of physics so the

usefulness of this conjecture is limited.

Barring discovery during current intensive efforts, it will be sometime after the end of the current physics fill at the

LHC in 2011 and some further months or years of analysis of the collected data before scientists can confidently

believe there is no such thing as a Higgs boson.

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Higgs boson 87

Alternatives for electroweak symmetry breaking

In the years since the Higgs boson was proposed, several alternatives to the Higgs mechanism have been proposed.

All of the alternative mechanisms use strongly interacting dynamics to produce a vacuum expectation value that

breaks electroweak symmetry. A partial list of these alternative mechanisms are

• Technicolor[25] is a class of models that attempts to mimic the dynamics of the strong force as a way of breaking

electroweak symmetry.• Extra dimensional Higgsless models where the role of the Higgs field is played by the fifth component of the

gauge field.[26]

• Abbott-Farhi models of composite W and Z vector bosons.[27]

• Top quark condensate.

• Braid model of Standard Model particles by Sundance Bilson-Thompson, compatible with loop quantum gravity

and similar theories.[28]

"The God particle"

The Higgs boson is often referred to as "the God particle" by the media,[29]

after the title of Leon Lederman's book,The God Particle: If the Universe Is the Answer, What Is the Question?.[30] While use of this term may have

contributed to increased media interest in particle physics and the Large Hadron Collider,[30] many scientists dislike

it.[29] In a renaming competition, a jury of physicists chose the name "the champagne bottle boson" as the best

popular name.[31]

See also

• List of particles

• Higgs mechanism

• Overview and Differences of 1964 PRL Symmetry Breaking papers

• Quantum triviality

• Yukawa interaction

• ZZ diboson

• Higgs boson in fiction

Notes

[1] "Huge $10 billion collider resumes hunt for 'God particle' - CNN.com" (http://www.  cnn. com/2009/TECH/11/11/lhc. large. hadron.

collider. beam/index. html). CNN . 2009-11-11. . Retrieved 2010-05-04.

[2] "Race for 'God particle' heats up" (http://news. bbc. co. uk/2/hi/science/nature/7893689. stm). BBC News. 2009-02-17. . Retrieved

2010-01-05.

[3] Englert-Brout-Higgs-Guralnik-Hagen-Kibble Mechanism on Scholarpedia (http://www.  scholarpedia. org/article/ Englert-Brout-Higgs-Guralnik-Hagen-Kibble_mechanism)

[4] Englert, François; Brout, Robert (1964). "Broken Symmetry and the Mass of Gauge Vector Mesons". Physical Review Letters 13: 321 –23.

doi:10.1103/PhysRevLett.13.321

[5] Higgs, Peter (1964). "Broken Symmetries and the Masses of Gauge Bosons". Physical Review Letters 13: 508 –509.

doi:10.1103/PhysRevLett.13.508

[6] Guralnik, Gerald; Hagen, C. R.; Kibble, T. W. B. (1964). "Global Conservation Laws and Massless Particles". Physical Review Letters 13:

585 –587. doi:10.1103/PhysRevLett.13.585

[7] Guralnik, Gerald S. (2009). "The History of the Guralnik, Hagen and Kibble development of the Theory of Spontaneous Symmetry Breaking

and Gauge Particles". International Journal of Modern Physics  A24: 2601 –2627. doi:10.1142/S0217751X09045431. arXiv:0907.3466

[8]  Physical Review Letters - 50th Anniversary Milestone Papers (http://prl.aps.org/50years/milestones#1964). Physical Review Letters.

[9] "American Physical Society - J. J. Sakurai Prize Winners" (http://www.  aps. org/units/dpf/awards/sakurai. cfm).

[10] A quasi-political Explanation of the Higgs Boson; for Mr Waldegrave, UK Science Minister 1993 (http://www. 

hep. 

ucl. 

ac. 

uk/~djm/ higgsa. html)

[11] T. Schücker (2007). "Higgs-mass predictions". arΧiv:0708.3344 [hep-ph].

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Higgs boson 88

[12] Scientists present first “bread-and-butter” results from LHC collisions (http://www.  symmetrymagazine. org/breaking/2010/06/08/ 

scientists-present-first-bread-and-butter-results-from-lhc-collisions/)Symmetry Breaking, 8 June 2010

[13] W.-M. Yao et al. (2006). Searches for Higgs Bosons "Review of Particle Physics" (http://pdg.  lbl. gov/2006/reviews/higgs_s055. pdf).

 Journal of Physics G 33: 1. doi:10.1088/0954-3899/33/1/001. Searches for Higgs Bosons.

[14] "CERN management confirms new LHC restart schedule" (http://press. web. cern. ch/press/PressReleases/Releases2009/PR02. 09E.

html). CERN Press Office. 9 February 2009. . Retrieved 2009-02-10.

[15] "CERN reports on progress towards LHC restart" (http://press.web.cern.  ch/press/PressReleases/Releases2009/PR09. 09E.  html).

CERN Press Office. 19 June 2009. . Retrieved 2009-07-21.[16] T. Aaltonen et al. (CDF and DØ Collaborations) (2010). "Combination of Tevatron searches for the standard model Higgs boson in the

W+W− decay mode". arΧiv:1001.4162 [hep-ex].

[17] "Fermilab experiments narrow allowed mass range for Higgs boson" (http://www.  fnal. gov/pub/presspass/press_releases/ 

Higgs-mass-constraints-20100726-images.html). Fermilab. 26 July 2010. . Retrieved 2010-07-26.

[18] CERN Bulletin Issue No. 18-20/2010 - Monday 3 May 2010 (http://cdsweb.cern.  ch/journal/CERNBulletin/2010/18/News Articles/ 

1262593?ln=en)

[19] " H0 Indirect Mass Limits from Electroweak Analysis. (http://pdglive. lbl.gov/popupblockdata. brl?nodein=S055HEW&inscript=Y&

fsizein=1)"

[20] Potential Higgs Boson discovery: " Higgs Boson: Glimpses of the God particle. (http://www. newscientist. com/channel/fundamentals/ 

mg19325934.  600-higgs-boson-glimpses-of-the-god-particle.html)" New Scientist, 02 March 2007

[21] " 'God particle' may have been seen, (http://news. bbc. co. uk/2/hi/science/nature/3546973. stm)" BBC news, 10 March 2004.

[22] US experiment hints at 'multiple God particles' (http://news. 

bbc. 

co. 

uk/1/hi/science_and_environment/10313875. 

stm) BBC News 14June 2010

[23] arXiv:0912.0004 Higgs in Space! (http://arxiv.org/abs/0912.  0004)

[24] Physics World, (http://physicsworld.com/cws/article/news/41218), a website supported by the British Institute of Physics

[25] S. Dimopoulos and Leonard Susskind (1979). "Mass Without Scalars". Nuclear Physics B 155: 237 –252.

doi:10.1016/0550-3213(79)90364-X.

[26] C. Csaki and C. Grojean and L. Pilo and J. Terning (2004). "Towards a realistic model of Higgsless electroweak symmetry breaking".

 Physical Review Letters 92: 101802. doi:10.1103/PhysRevLett.92.101802. arXiv:hep-ph/0308038.

[27] L. F. Abbott and E. Farhi (1981). "Are the Weak Interactions Strong?". Physics Letters B 101: 69. doi:10.1016/0370-2693(81)90492-5.

[28] Bilson-Thompson, Sundance O.; Markopoulou, Fotini; Smolin, Lee (2007). "Quantum gravity and the standard model". Class. Quantum

Grav. 24 (16): 3975 –3993. doi:10.1088/0264-9381/24/16/002. arXiv:hep-th/0603022.

[29] Ian Sample (29 May 2009). "Anything but the God particle" (http://www.guardian. co. uk/science/blog/2009/may/29/ 

why-call-it-the-god-particle-higgs-boson-cern-lhc). London: The Guardian. . Retrieved 2009-06-24.

[30] Ian Sample (3 March 2009). "Father of the God particle: Portrait of Peter Higgs unveiled" (http://www.  guardian. co. uk/science/blog/ 

2009/mar/02/god-particle-peter-higgs-portrait-lhc). London: The Guardian. . Retrieved 2009-06-24.

[31] Sample, Ian (2009-06-12). "Higgs competition: Crack open the bubbly, the God particle is dead" (http://www. guardian. co. uk/science/ 

blog/2009/jun/05/cern-lhc-god-particle-higgs-boson).The Guardian (London). . Retrieved 2010-05-04.

References

• " The LEP Electroweak Working Group. (http://lepewwg. web. cern. ch/LEPEWWG/)"

• " Particle Data Group: Review of searches for Higgs bosons. (http://pdg. lbl. gov/2005/reviews/ 

contents_sports. html#hyppartetc)"

• Leon Lederman and Dick Teresi, 1993. The God Particle: If the Universe Is the Answer, What Is the Question?

Houghton Mifflin Co. ISBN 0-395-55849-2, paperback ISBN 0-385-31211-3.• " Fermilab Results Change Estimated Mass Of Postulated Higgs boson. (http://www. spacedaily. com/news/ 

physics-04s. html)"

• " Higgs boson on the horizon. (http://physicsweb. org/article/news/4/9/2/1)"

• " Signs of mass-giving particle get stronger. (http://www.sciencenews. org/articles/20001104/fob6.asp)"

• " Higgs boson: One page explanation. (http://www.phy.uct. ac.za/courses/phy400w/particle/higgs.  htm)" In

1993, the UK Science Minister, William Waldegrave, challenged physicists to produce a one page answer to the

question "What is the Higgs boson, and why do we want to find it?"

• " Higgs mechanism/boson simple explanation via cartoon. (http://www. pparc. ac. uk/ps/bbs/bbs_mass_hm.

asp)"

• " Higgs physics at the LHC. (http://www. quark.lu.  se/~atlas/thesis/egede/thesis-node6.html)"• " Quark experiment predicts heavier Higgs. (http://www.newscientist.com/news/news.jsp?id=ns99995095)"

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Higgs boson 89

• Martin, Richard, " The God Particle and the Grid. (http://www. wired. com/wired/archive/12.  04/grid_pr.

html)"

• " The Higgs boson (http://www. exploratorium. edu/origins/cern/ideas/higgs.  html)" by the CERN

exploratorium.

• " Higgs Boson - the search for the God particle. (http://www.bbc. co.uk/radio4/history/inourtime/ 

inourtime_20041118. shtml)" BBC Radio 4: "In Our Time"

Further reading

• G.S. Guralnik, C.R. Hagen and T.W.B. Kibble (1964). "Global Conservation Laws and Massless Particles".

 Physical Review Letters 13: 585. doi:10.1103/PhysRevLett.13.585.

• F. Englert and R. Brout (1964). "Broken Symmetry and the Mass of Gauge Vector Mesons". Physical Review

 Letters 13: 321. doi:10.1103/PhysRevLett.13.321.

• P. Higgs (1964). "Broken Symmetries, Massless Particles and Gauge Fields". Physics Letters 12: 132.

doi:10.1016/0031-9163(64)91136-9.

• P. Higgs (1964). "Broken Symmetries and the Masses of Gauge Bosons". Physical Review Letters 13: 508.

doi:10.1103/PhysRevLett.13.508.• P. Higgs (1966). "Spontaneous Symmetry Breakdown without Massless Bosons". Physical Review 145: 1156.

doi:10.1103/PhysRev.145.1156.

• Y. Nambu and G. Jona-Lasinio (1961). "Dynamical Model of Elementary Particles Based on an Analogy with

Superconductivity". Physical Review 122: 345 –358. doi:10.1103/PhysRev.122.345.

• J. Goldstone, A. Salam and S. Weinberg (1962). "Broken Symmetries". Physical Review 127: 965.

doi:10.1103/PhysRev.127.965.

• P.W. Anderson (1963). "Plasmons, Gauge Invariance, and Mass". Physical Review 130: 439.

doi:10.1103/PhysRev.130.439.

• A. Klein and B.W. Lee (1964). "Does Spontaneous Breakdown of Symmetry Imply Zero-Mass Particles?".

 Physical Review Letters 12: 266. doi:10.1103/PhysRevLett.12.266.• W. Gilbert (1964). "Broken Symmetries and Massless Particles". Physical Review Letters 12: 713.

doi:10.1103/PhysRevLett.12.713.

External links

• Explanation for beginners (http://cms. web.cern.ch/cms/Physics/HuntingHiggs/index.  html)

• At Fermilab, the Race Is on for the 'God Particle' (http://www. nytimes. com/2007/07/24/science/24ferm.

html)

• Physics World, Introducing the little Higgs (http://physicsworld.com/cws/article/print/11353)

• A quasi-political Explanation of the Higgs Boson (http://www. 

hep. 

ucl. 

ac. 

uk/~djm/higgsa.html)• The Atom Smashers, a blog about the making of a documentary about the search for the Higgs boson (http:// 

www. theatomsmashers. blogspot. com/)

• In CERN Courier, Steven Weinberg reflects on spontaneous symmetry breaking (http://cerncourier.com/cws/ 

article/cern/32522)

• Steven Weinberg Praises Teams for Higgs Boson Theory (http://www. pas. rochester. edu/urpas/news/ 

Hagen_030708)

• Steven Weinberg on LHC (http://www.youtube. com/watch?v=Zl4W3DYTIKw)

• Physical Review Letters - 50th Anniversary Milestone Papers (http://prl.aps. org/50years/milestones#1964)

• Imperial College London on PRL 50th Anniversary Milestone Papers (http://www3.imperial. ac. uk/ 

newsandeventspggrp/imperialcollege/newssummary/news_13-6-2008-12-42-20?newsid=38514)

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Higgs boson 90

• The God Particle, from National Geographic Magazine (http://ngm.nationalgeographic.  com/2008/03/ 

god-particle/achenbach-text)

• "Tevatron experiments double-team Higgs boson", sets lower bound at 170GeV (http://www.physorg. com/ 

news137076565. html)

• The History of the Guralnik, Hagen and Kibble development of the Theory of Spontaneous Symmetry Breaking

and Gauge Particles (http://arxiv.org/abs/0907.  3466)

• The History of the Guralnik, Hagen and Kibble development of the Theory of Spontaneous Symmetry Breaking

and Gauge Particles (PDF) (http://arxiv. org/abs/0907.  3466v1)

• Englert-Brout-Higgs-Guralnik-Hagen-Kibble Mechanism on Scholarpedia (http://www. scholarpedia. org/ 

article/Englert-Brout-Higgs-Guralnik-Hagen-Kibble_mechanism)

• History of Englert-Brout-Higgs-Guralnik-Hagen-Kibble Mechanism on Scholarpedia (http://www. scholarpedia.

org/article/Englert-Brout-Higgs-Guralnik-Hagen-Kibble_mechanism_(history))

• Sakurai Prize Videos (http://www.youtube. com/view_play_list?p=BDA16F52CA3C9B1D)

• God Particle Overview (http://www. godparticle.com/)

• Fermilab 'closing in' on the God particle (http://www.newscientist. com/article/ 

dn16618-fermilab-closing-in-on-the-god-particle.html)• The Hunt for the Higgs at Tevatron (http://apps3. aps. org/aps/meetings/april10/roser.  pdf)

• Artist's vision of Higgs boson by a Prague based fine art photographer Jan Krasňan (from his series created in

January 2009) (http://krasnan.com/abstract. pdf)

• In Our Time:Higgs Boson (http://www. bbc. co. uk/programmes/p004y2b7) BBC Radio 4 programme

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91

Safety

Safety of particle collisions at the Large HadronCollider

A simulated particle collision in the LHC.

The safety of particle collisions at the Large Hadron

Collider has been questioned in the media, on the

Internet and through the courts. Particle physics

experiments were ongoing as of March 2010 at the

Large Hadron Collider (LHC), the world's largest and

most powerful particle accelerator, built by the

European Organization for Nuclear Research (CERN)near Geneva, in Switzerland.[1] [2] The claimed dangers

of the LHC particle collisions, which began in

November 2009, include doomsday scenarios involving

the production of stable micro black holes and the

creation of hypothetical particles called strangelets.[3]

To address such concerns, CERN mandated a group of 

independent scientists to review these scenarios. In a

report issued in 2003, they concluded that, like current

particle experiments such as the Relativistic Heavy Ion

Collider (RHIC), the LHC particle collisions pose no conceivable threat. [4] A second review of the evidence

commissioned by CERN was released in 2008. The report, prepared by a group of physicists affiliated to CERN but

not involved in the LHC experiments, reaffirmed the safety of the LHC collisions in light of further research

conducted since the 2003 assessment.[5]  [6] It was reviewed and endorsed by a CERN committee of 20 external

scientists and by the Executive Committee of the Division of Particles & Fields of the American Physical Society, [7]

[8] and was later published in the peer-reviewed  Journal of Physics G by the UK Institute of Physics, which also

endorsed its conclusions.[5] [9] The report ruled out any doomsday scenario at the LHC: the physical conditions and

events that will be created in the LHC experiments occur naturally in the universe without hazardous

consequences.[5]

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Safety of particle collisions at the Large Hadron Collider 92

Particle accelerator

The LHC's CMS detector.

The Large Hadron Collider (LHC) is the world's largest and highest-energy

particle accelerator complex, intended to collide opposing beams of either

protons or lead nuclei with very high kinetic energy.[10]  [11] It was built by the

European Organization for Nuclear Research (CERN) near Geneva, in

Switzerland. The LHC's main purpose is to explore the validity and limitations of the Standard Model, the current theoretical picture for particle physics. The first

particle collisions at the LHC took place shortly after startup in November 2009,

at energies up to 1.2 TeV per beam.[12] .

On 30 March 2010, the first planned collisions took place between two 3.5 TeV

beams, which set another new world record for the highest energy man-made

particle collisions.[13]

Due to problematic connections between the superconducting magnets that guide

the beams, the LHC will not run at its designed 7 TeV per beam (14 TeV

center-of-mass) until after a long shutdown that is scheduled to begin at the end of 2011.[14]

Safety concerns

In the run up to the commissioning of the LHC, Walter L. Wagner (an original opponent of the RHIC), Lu is Sancho

(a Spanish science writer) and Otto Rössler (a German biochemist) have expressed concerns over the safety of the

LHC, and have attempted to halt the beginning of the experiments through petitions to the US and European

Courts.[1] [15] [16] [17] [18] These opponents assert that the LHC experiments have the potential to create low velocity

micro black holes that could grow in mass or release dangerous radiation leading to doomsday scenarios, such as the

destruction of the Earth.[3]  [19] Other claimed potential risks include the creation of theoretical particles called

strangelets, magnetic monopoles and vacuum bubbles.

[3]

 

[19]

Based on such safety concerns, US federal judge Richard Posner[20] , Future of Humanity Institute research associate

Toby Ord[21] and others[22] [23] [24] [25] have argued that the LHC experiments are too risky to undertake. In the book

Our Final Century: Will the Human Race Survive the Twenty-first Century? , English cosmologist and astrophysicist

Martin Rees calculated an upper limit of 1 in 50 million for the probability that the Large Hadron Collider will

produce a global catastrophe or black hole.[15] However, Rees has also reported not to be "losing sleep over the

collider," and trusts the scientists who have built it.[26] He has stated: "My book has been misquoted in one or two

places. I would refer you to the up-to-date safety study."[27]

These risk assessments of catastrophic scenarios at the LHC have sparked fears among the public, [1] and scientists

associated with the project have received protests. The Large Hadron Collider team revealed that they had received

death threats and threatening emails and phone calls demanding the experiment be halted.[27] On 9 September 2008,Romania's Conservative Party held a protest before the European Commission mission to Bucharest, demanding that

the experiment be halted because it feared that the LHC could create dangerous black holes.[28] [29]

Media coverage of safety concerns

The safety concerns regarding the LHC collisions have attracted widespread media attention. [1] [30] Various widely

circulated newspapers have reported doomsday fears in connection with the collider, including The Times,[31] The

Guardian,[32] The Independent ,[33] The Sydney Morning Herald ,[34] and Time.[35] Among other media sources, CNN

mentioned that "Some have expressed fears that the project could lead to the Earth's demise," [36] but it assured its

readers with comments from scientists like John Huth, who said that it was "baloney".[36]

MSNBC said that, "thereare more serious things to worry about"[37] and allayed fears that "the atom-smasher might set off earthquakes or

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Safety of particle collisions at the Large Hadron Collider 93

other dangerous rumblings".[37] The results of an online survey it conducted "indicate that a lot of [the public] know

enough not to panic".[37] The BBC stated, "the scientific consensus appears to be on the side of CERN's theorists"[38]

who say the LHC has "no conceivable danger".[38] Brian Greene in the   New York Times reassured readers by

saying,"If a black hole is produced under Geneva, might it swallow Switzerland and continue on a ravenous rampage

until the earth is devoured? It’s a reasonable question with a definite answer: no."[39]

The tabloids also covered the safety concerns. The  Daily Mail produced headlines such as "Are we all going to dienext Wednesday?"[40] and "End of the world postponed as broken Hadron Collider out of commission until the

spring"[41] . The Sun quoted Otto Rössler saying, "The weather will change completely, wiping out life. There will

be a Biblical Armageddon."[42] After the launch of the collider, it had a story entitled, "Success! The world hasn't

ended".[43]

On 10 September 2008, a 16-year-old girl from Sarangpur, Madhya Pradesh, India committed suicide, having

become distressed about predictions of an impending "doomsday" made on an Indian news channel (Aaj Tak)

covering the LHC.[44]

After the dismissal of the federal lawsuit, The Daily Show's correspondent John Oliver interviewed Walter L.

Wagner, who declared that he believed the chance of the LHC destroying the earth to be 50%, since it will either

happen or it won't.[45] [46]

Safety reviews

Concerns similar to those for the LHC were raised in connection with the RHIC particle accelerator.[47] [48] [49] [50]

After detailed studies, scientists reached such conclusions as "beyond reasonable doubt, heavy-ion experiments at

RHIC will not endanger our planet"[51] and that there is "powerful empirical evidence against the possibility of 

dangerous strangelet production."[52]

CERN-commissioned reports

Drawing from research performed to assess the safety of the RHIC collisions, the LHC Safety Study Group, a groupof independent scientists, performed a safety analysis of the LHC, and released their findings in the 2003 report

Study of Potent ially Dangerous Events During Heavy-Ion Collisions at the LHC . The report concluded that there is

"no basis for any conceivable threat".[4] Several of its arguments were based on the predicted evaporation of 

hypothetical micro black holes by Hawking radiation and on the theoretical predictions of the Standard Model with

regard to the outcome of events to be studied in the LHC. One argument raised against doomsday fears was that

collisions at energies equivalent to and higher than those of the LHC have been happening in nature for billions of 

years apparently without hazardous effects, as ultra-high-energy cosmic rays impact Earth's atmosphere and other

bodies in the universe.[4]

In 2007, CERN mandated a group of five particle physicists not involved in the LHC experiments — the LHC Safety

Assessment Group (LSAG), consisting of John Ellis, Gian Giudice, Michelangelo Mangano and Urs Wiedemann, of 

CERN, and Igor Tkachev, of the Institute for Nuclear Research in Moscow — to monitor the latest concerns about

the LHC collisions.[6] On 20 June 2008, in light of new experimental data and theoretical understanding, the LSAG

issued a report updating the 2003 safety review, in which they reaffirmed and extended its conclusions that "LHC

collisions present no danger and that there are no reasons for concern".[5] [6] The LSAG report was then reviewed by

CERN’s Scientific Policy Committee (SPC), a group of external scientists that advises CERN ’s governing body, its

Council.[7]  [17]  [53] The report was reviewed and endorsed by a panel of five independent scientists, Peter

Braun-Munzinger, Matteo Cavalli-Sforza, Gerard 't Hooft, Bryan Webber and Fabio Zwirner, and their conclusions

were unanimously approved by the full 20 members of the SPC.[53] On 5 September 2008, the LSAG's "Review of 

the safety of LHC collisions" was published in the  Journal of Physics G: Nuclear and Particle Physics by the UK

Institute of Physics, which endorsed its conclusions in a press release that announced the publication.[5] [9]

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Following the July 2008 release of the LSAG safety report,[5] the Executive Committee of the Division of Particles

and Fields (DPF) of the American Physical Society, the world's second largest organization of physicists, issued a

statement approving the LSAG's conclusions and noting that "this report explains why there is nothing to fear from

particles created at the LHC".[8] On 1 August 2008, a group of German quantum physicists, the Committee for

Elementary Particle Physics (KET),[54] published an open letter further dismissing concerns about the LHC

experiments and carrying assurances that they are safe based on the LSAG safety review.[2] [55]

Other publications

On 20 June 2008, Steven Giddings and Michelangelo Mangano issued a research paper titled the "Astrophysical

implications of hypothetical stable TeV-scale black holes", where they develop arguments to exclude any risk of 

dangerous black hole production at the LHC.[56] On 18 August 2008, this safety review was published in the

  Physical Review D,[57] and a commentary article which appeared the same day in the journal  Physics endorsed

Giddings' and Mangano's conclusions.[58] The LSAG report draws heavily on this research.[17]

On 9 February 2009, a paper titled "Exclusion of black hole disaster scenarios at the LHC" was published in the

 journal   Physics Letters B.[59] The article, which summarizes proofs aimed at ruling out any possible black hole

disaster at the LHC, relies on a number of new safety arguments as well as certain arguments already present inGiddings' and Mangano's paper "Astrophysical implications of hypothetical stable TeV-scale black holes".[56]

Safety arguments

Micro black holes

Although the Standard Model of particle physics predicts that LHC energies are far too low to create black holes,

some extensions of the Standard Model posit the existence of extra spatial dimensions, in which it would be possible

to create micro black holes at the LHC at a rate of the order of one per second.[60] [61] [62] [63] [64] According to the

standard calculations these are harmless because they would quickly decay by Hawking radiation.

[62]

Hawkingradiation is a thermal radiation predicted to be emitted by black holes due to quantum effects. Because Hawking

radiation allows black holes to lose mass, black holes that lose more matter than they gain through other means are

expected to dissipate, shrink, and ultimately vanish. Smaller micro black holes (MBHs), which could be produced at

the LHC, are currently predicted by theory to be larger net emitters of radiation than larger black holes, and to shrink

and dissipate instantly.[65] The LHC Safety Assessment Group (LSAG) indicates that "there is broad consensus

among physicists on the reality of Hawking radiation, but so far no experiment has had the sensitivity required to

find direct evidence for it."[5]

According to the LSAG, even if micro black holes were produced by the LHC and were stable, they would be unable

to accrete matter in a manner dangerous for the Earth. They would also have been produced by cosmic rays and have

stopped in neutron stars and white dwarfs, and the stability of these astronomical bodies means that they cannot bedangerous:[5] [66]

Stable black holes could be either electrically charged or neutral. [...] If stable microscopic black holes had no

electric charge, their interactions with the Earth would be very weak. Those produced by cosmic rays would

pass harmlessly through the Earth into space, whereas those produced by the LHC could remain on Earth.

However, there are much larger and denser astronomical bodies than the Earth in the Universe. Black holes

produced in cosmic-ray collisions with bodies such as neutron stars and white dwarf stars would be brought to

rest. The continued existence of such dense bodies, as well as the Earth, rules out the possibility of the LHC

producing any dangerous black holes.[6]

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Strangelets

Strangelets are small fragments of strange matter —a hypothetical form of quark matter —that contain roughly equal

numbers of up, down, and strange quarks and that are more stable than ordinary nuclei (strangelets would range in

size from a few femtometers to a few meters across).[5] If strangelets can actually exist, and if they were produced at

the LHC, they could conceivably initiate a runaway fusion process in which all the nuclei in the planet would be

converted to strange matter, similar to a strange star.[5]

The probability of the creation of strangelets decreases at higher energies.[5] As the LHC operates at higher energies

than the RHIC or the heavy ion programs of the 1980s and 1990s, the LHC is less likely to produce strangelets than

its predecessors.[5] Furthermore, models indicate that strangelets are only stable or long-lived at low temperatures.

Strangelets are bound at low energies (in the range of 1 –10 MeV), while the collisions in the LHC release energies in

the range of 14 TeV. The second law of thermodynamics precludes the formation of a cold condensate that is an

order of magnitude cooler than the surrounding medium. This can be illustrated by the example of trying to form an

ice cube in boiling water.[5]

Specific concerns and responses

Otto Rössler, a German chemistry professor at the University of Tübingen, argues that micro black holes created in

the LHC could grow exponentially.[67]  [68]  [69]  [70]  [71] On 4 July 2008, Rössler met with a CERN physicist, Rolf 

Landua, with whom he discussed his safety concerns.[72] Following the meeting, Landua asked another expert,

Hermann Nicolai, Director of the Albert Einstein Institute, in Germany, to examine Rössler's arguments.[72] Nicolai

reviewed Otto Rössler's research paper on the safety of the LHC[68] and issued a statement highlighting logical

inconsistencies and physical misunderstandings in Rössler's arguments.[73] Nicolai concluded that "this text would

not pass the referee process in a serious journal."[71] [73] Domenico Giulini also commented with Hermann Nicolai

on Otto Rössler's thesis, concluding that "his argument concerns only the General Theory of Relativity (GRT), and

makes no logical connection to LHC physics; the argument is not valid; the argument is not self-consistent."[74] On 1

August 2008, a group of German physicists, the Committee for Elementary Particle Physics (KET),[54]

published anopen letter further dismissing Rössler's concerns and carrying assurances that the LHC is safe.[2]  [55] Otto Rössler

was due to meet Swiss president Pascal Couchepin in August 2008 to discuss this concern,[75] but it was later

reported that the meeting had been canceled as it was believed Rössler and his fellow opponents would have used the

meeting for their own publicity.[76]

On 10 August 2008, Rainer Plaga, a German astrophysicist, posted a research paper on the arXiv Web archive

concluding that LHC safety studies have not definitely ruled out the potential catastrophic threat from microscopic

black holes, including the possible danger from Hawking radiation emitted by black holes. [3]  [77]  [78]  [79] In a

follow-up paper posted on the arXiv on 29 August 2008, Steven Giddings and Michelangelo Mangano, the authors

of the research paper "Astrophysical implications of hypothetical stable TeV-scale black holes", [56] responded to

Plaga's concerns.[80] They pointed out what they see as a basic inconsistency in Plaga's calculation, and argued thattheir own conclusions on the safety of the collider, as referred to in the LHC safety assessment (LSAG) report, [5]

remain robust.[80] Giddings and Mangano also referred to the research paper "Exclusion of black hole disaster

scenarios at the LHC", which relies on a number of new arguments to conclude that there is no risk due to mini black

holes at the LHC.[3]  [59] . On 19 January 2009 Roberto Casadio, Sergio Fabi and Benjamin Harms posted on the

arXiv a paper, later published on Physical Review D, ruling out the catastrophic growth of black holes in the scenario

considered by Plaga.[81] In reaction to the criticisms, Plaga updated his paper on the arXiv on 26 September 2008

and again on 9 August 2009.[77] So far, Plaga's paper has not been published in a peer-reviewed journal.

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Legal challenges

On 21 March 2008, a complaint requesting an injunction to halt the LHC's startup was filed by Walter L. Wagner

and Luis Sancho against CERN and its American collaborators, the US Department of Energy, the National Science

Foundation and the Fermi National Accelerator Laboratory, before the United States District Court for the District of 

Hawaii.[19] [82] [83] The plaintiffs demanded an injunction against the LHC's activation for 4 months after issuance of 

the LHC Safety Assessment Group's (LSAG) most recent safety documentation, and a permanent injunction until theLHC can be demonstrated to be reasonably safe within industry standards.[84] The US Federal Court scheduled trial

to begin 16 June 2009.[85]

The LSAG review, issued on 20 June 2008 after outside review, found "no basis for any concerns about the

consequences of  new particles or forms of matter that could possibly be produced by the LHC".[5] The US

Government, in response, called for summary dismissal of the suit against the government defendants as untimely

due to the expiration of a six-year statute of limitations (since funding began by 1999 and has essentially been

completed already), and also called the hazards claimed by the plaintiffs "overly speculative and not credible".[86]

The Hawaii District Court heard the government's motion to dismiss on 2 September 2008,[1] and on 26 September

the Court issued an order granting the motion to dismiss on the grounds that it had no jurisdiction over the LHC

project.[87] A subsequent appeal by the plaintiffs was dismissed by the Court on 24 August 2010.[88]

On 26 August 2008, a group of European citizens, led by a German biochemist Otto Rössler, filed a suit against

CERN in the European Court of Human Rights in Strasbourg.[69] The suit, which was summarily rejected on the

same day, alleged that the Large Hadron Collider posed grave risks for the safety of the 27 member states of the

European Union and their citizens.[31] [35] [69]

Late in 2009 a review of the legal situation by Eric Johnson, a lawyer, was published in the Tennessee Law

 Review.[89]  [90]  [91] In February 2010 a summary of Johnson's article appeared as an opinion piece in New

Scientist.[92]

In February 2010, the German Constitutional Court (Bundesverfassungsgericht) rejected an injunction petition to

halt the LHC's operation as unfounded, without hearing the case, stating that the opponents had failed to produceplausible evidence for their theories.[93]

References

[1] Boyle, Alan (2 September 2008). " Courts weigh doomsday claims (http://cosmiclog. msnbc.  msn.  com/archive/2008/09/02/1326534.

aspx)". Cosmic Log. msnbc.com.

[2] Hawley, Charles (6 August 2008). " Physicists Allay Fears of the End of the World (http://www. spiegel. de/international/world/ 

0,1518,570487,00. html)". Spiegel Online.

[3] Boyle, Alan (19 August 2008). " Twists in the Doomsday debate (http://cosmiclog. msnbc.  msn.  com/archive/2008/08/19/1276192.

aspx?Ajax_CallBack=true)". Cosmic Log. msnbc.com.

[4] Blaizot JP, Iliopoulos J, Madsen J, Ross GG, Sonderegger P, Specht HJ (2003). Study of Potentially Dangerous Events During Heavy-Ion

Collisions at the LHC (http://doc.  cern.ch/yellowrep/2003/2003-001/p1.pdf) (PDF, 176 KiB). CERN. Geneva. CERN-2003-001 (http:// cdsweb. cern. ch/search?sysno=002372601cer).

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LHC Collisions (http://arxiv. org/pdf/0806. 3414)" (PDF, 586 KiB). ''Journal of Physics G: Nuclear and Particle Physics. 35, 115004

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Safety of particle collisions at the Large Hadron Collider 97

[11] Achenbach, Joel (1 March 2008). " The God Particle (http://ngm. nationalgeographic. com/2008/03/god-particle/achenbach-text)".

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symmetrymagazine. org/breaking/2010/02/01/cerns-new-lhc-plan-two-years-at-3-5-tev/)"[15] " Some fear debut of powerful atom-smasher (http://edition. cnn. com/2008/TECH/06/30/doomsdaycollider. ap/index. html)"

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21cernw. html)". The New York Times.

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3349v2) (PDF). Physics Letters B. 672 (1): 71 –76. doi:10.1016/j.physletb.2009.01.003. arXiv:0807.3349. CERN record (http://cdsweb.  cern.

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[66] Schewe, Phil (9 September 2008). " Mini Black Holes No Danger (http://www.aip. org/pnu/2008/split/871-1. html)". Inside Science

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spiritualottoeroessler. pdf)" (PDF, 24 KiB).

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news/worldnews/europe/2650665/Legal-bid-to-stop-CERN-atom-smasher-from-destroying-the-world. html)". Telegraph.co.uk .

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[72] Schmidt, Von Wolf (7 September 2008). " Der Prophet des Planetentods (http://www.  taz. de/1/zukunft/wissen/artikel/1/ 

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[74] Giulini, Domenico; and Nicolai, Hermann (August 2008). On the arguments of O.E. Rössler (http://environmental-impact. web. cern. ch/ environmental-impact/Objects/LHCSafety/NicolaiFurtherComment-en.pdf) (PDF, 96 KiB).

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roessler_schwarze_loecher_cern_couchepin_1.789024.html)" (in German). NZZ Online. 21 July 2008.

[76] " Kein Gespräch zwischen Couchepin und Cern-Kritiker (http://www. nzz.ch/nachrichten/wissenschaft/ 

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[78] Clery, Daniel; & Cho, Adrian (5 September 2008). "Large Hadron Collider: Is the LHC a Doomsday Machine?" Science. Vol. 321. no.

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[79] Brean, Joseph (9 September 2008). " Is the end nigh? Science experiment could swallow Earth, critics say (http://www.  nationalpost. com/ 

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[80] Giddings, Steven B.; & Mangano, Michelangelo L. (29 August 2008). Comments on claimed risk from metastable black holes (http://arxiv.org/pdf/0808. 4087v1) (PDF). arXiv:0808.4087. CERN-PH-TH/2008-184.

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External links

• "The safety of the LHC" (http://public. web.cern.  ch/public/en/LHC/Safety-en.  html), CERN webpage.

• "The LHC is safe" (video) (http://cdsweb.cern. ch/record/1120625?ln=en), talk by John Ellis at CERN, on 14

August 2008.

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Micro black hole 100

Micro black hole

 MBH redirects here. It can also refer to the Hayist Bases Movement, or a unit of power - a thousand BTUs

 per hour.

Micro black holes are tiny black holes, also called quantum mechanical black holes or mini black holes, for

which quantum mechanical effects play an important role.[1]

It is possible that such quantum primordial black holes were created in the high-density environment of the early

Universe (or big bang), or possibly through subsequent phase transitions. They might be observed by astrophysicists

in the near future, through the particles they are expected to emit by Hawking radiation.

Some theories involving additional space dimensions predict that micro black holes could be formed at an energy as

low as the TeV range, which will be available in particle accelerators such as the LHC (Large Hadron Collider).

Popular concerns have then been raised over end-of-the-world scenarios (see Safety of particle collisions at the Large

Hadron Collider). However, such quantum black holes would instantly evaporate, either totally or leaving only a

very weakly interacting residue. Beside the theoretical arguments, we can notice that the cosmic rays bombarding the

Earth do not produce any damage, although they reach center of mass energies in the range of hundreds of TeV.

Minimum mass of a black hole

In principle, a black hole can have any mass above the Planck mass. To make a black hole, one must concentrate

mass or energy sufficiently that the escape velocity from the region in which it is concentrated exceeds the speed of 

light. This condition gives the Schwarzschild radius, , where G is Newton's constant and c is the

speed of light, as the size of a black hole of mass M. On the other hand, the Compton wavelength, ,

where h is Planck's constant, represents a limit on the minimum size of the region in which a mass M at rest can be

localized. For sufficiently small M, the reduced Compton wavelength ( , where ħ is Dirac's constant)

exceeds half the Schwarzschild radius, and no black hole description exists. This smallest mass for a black hole isthus approximately the Planck mass.Some extensions of present physics posit the existence of extra dimensions of space. In higher-dimensional

spacetime, the strength of gravity increases more rapidly with decreasing distance than in three dimensions. With

certain special configurations of the extra dimensions, this effect can lower the Planck scale to the TeV range.

Examples of such extensions include large extra dimensions, special cases of the Randall-Sundrum model, and

String theory configurations like the GKP solutions. In such scenarios, black hole production could possibly be an

important and observable effect at the LHC.[1] [2] [3] [4] [5] It would also be a common natural phenomenon induced

by the cosmic rays.

Stability of a micro black hole

Hawking radiation

In 1974 Stephen Hawking argued that due to quantum effects, black holes "evaporate" by a process now referred to

as Hawking Radiation in which elementary particles (photons, electrons, quarks, gluons, etc.) are emitted.[6] His

calculations show that the smaller the size of the black hole, the faster the evaporation rate, resulting in a sudden

burst of particles as the micro black hole suddenly explodes.

Any primordial black hole of sufficiently low mass will Hawking evaporate to near the Planck mass within the

lifetime of the Universe. In this process, these small black holes radiate away matter. A rough picture of this is that

pairs of virtual particles emerge from the vacuum near the event horizon, with one member of a pair being captured,

and the other escaping the vicinity of the black hole. The net result is the black hole loses mass (due to conservation

of energy). According to the formulae of black hole thermodynamics, the more the black hole loses mass the hotter it

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Micro black hole 101

becomes, and the faster it evaporates, until it approaches the Planck mass. At this stage a black hole would have a

Hawking temperature of TP

  / 8π (5.6×1032 K), which means an emitted Hawking particle would have an energy

comparable to the mass of the black hole. Thus a thermodynamic description breaks down. Such a mini-black hole

would also have an entropy of only 4π nats, approximately the minimum possible value. At this point then, the

object can no longer be described as a classical black hole, and Hawking's calculations also break down.

While Hawking radiation is sometimes questioned,[7]

Leonard Susskind summarizes an expert perspective in hisrecent book:[8] "Every so often, a physics paper will appear claiming that black holes don't evaporate. Such papers

quickly disappear into the infinite junk heap of fringe ideas."

Conjectures for the final state

Conjectures for the final fate of the black hole include total evaporation and production of a Planck mass-sized black

hole remnant. It is possible that such Planck-mass black holes, no longer able either to absorb energy gravitationally

like a classical black hole because of the quantised gaps between their allowed energy levels, nor to emit Hawking

particles for the same reason, may in effect be stable objects. In such case, they would be WIMPs (weakly

interacting massive particles); this could explain dark matter.

Primordial black holes

Formation in the early Universe

Production of a black hole requires concentration of mass or energy within the corresponding Schwarzschild radius.

It is hypothesized that shortly after the big bang the Universe was dense enough to fit within its own Schwarzschild

radius. Even so, at that time the Universe was not able to collapse into a singularity due to its uniform mass

distribution and rapid growth. This, however, does not fully exclude the possibility that black holes of various sizes

may have emerged locally. A black hole formed in this way is called a primordial black hole and is the most widely

accepted theory for the possible creation of micro black holes.

Expected observable effects

Primordial black holes of initial masses around 1015 grams would be completing their evaporation today; lighter

primordial black holes would have already evaporated.[1] In optimistic circumstances, the Fermi Gamma-ray Space

Telescope satellite, launched in June 2008, might detect experimental evidence for evaporation of nearby black holes

by observing gamma ray bursts.[9]  [10]  [11] It is unlikely that a collision between a microscopic black hole and an

object such as a star or a planet would be noticeable. This is due to the fact that the small radius and high density of 

the black hole would allow it to pass straight through any object consisting of normal atoms, interacting with only

few of its atoms while doing so. It has, however, been suggested that a small black hole (of sufficient mass) passing

through the Earth would produce a detectable acoustic or seismic signal.[12]

 [13]

 [14]

 [15]

Manmade micro black holes

Can we produce micro black holes?

In familiar three-dimensional gravity, the minimum energy of a microscopic black hole is 1019 GeV, which would

have to be condensed into a region on the order of the Planck length. This is far beyond the limits of any current

technology. It is estimated that to collide two particles to within a distance of a Planck length with currently

achievable magnetic field strengths would require a ring accelerator about 1000 light years in diameter to keep the

particles on track. Stephen Hawking also said in chapter 6 of his  Brief History of Time that physicist John Archibald

Wheeler once calculated that a very powerful hydrogen bomb using all the deuterium in all the water on Earth could

also generate such a black hole, but Hawking does not provide this calculation or any reference to it to support this

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assertion.

However, in some scenarios involving extra dimensions of space, the Planck mass can be as low as the TeV range.

The Large hadron collider (LHC) has a design energy of 14 TeV for proton-proton collisions and 1150 TeV for

Pb-Pb collisions. In these circumstances, it was argued in 2001 that black hole production could be an important and

observable effect at the LHC [2]  [3]  [4]  [5]  [16] or future higher-energy colliders. Such quantum black holes should

decay emitting sprays of particles that could be seen by detectors at these facilities.[2]

 [3]

A recent paper by Choptuikand Pretorius, published on March 17, 2010 in  Physical Review Letters presents a computer-generated proof that

micro black holes must form from two colliding particles with sufficient energy, which might be allowable at the

energies of the LHC if additional dimensions are present other than the customary four (three space, one time).[17]

[18]

Safety arguments

Hawking's calculation[6] and more general quantum mechanical arguments predict that micro black holes evaporate

almost instantaneously. Additional safety arguments beyond those based on Hawking radiation were given in the

paper [19]  [20] , which showed that in hypothetical scenarios with stable black holes that could damage Earth, such

black holes would have been produced by cosmic rays and would have already destroyed known astronomicalobjects such as the Earth, Sun, neutron stars, or white dwarfs. Further, microscopic black holes generated from a

particle accelerator are very small in size and are expected to have a high velocity, making it impossible for them to

accrete a dangerously large amount of mass before leaving the earth for good.

Black holes in quantum theories of gravity

It is possible, in some theories of quantum gravity, to calculate the quantum corrections to ordinary, classical black

holes. Contrarily to conventional black holes which are solutions of gravitational field equations of the general

theory of relativity, quantum gravity black holes incorporate quantum gravity effects in the vicinity of the origin,

where classical a curvature singularity occurs. According to the theory employed to model quantum gravity effects,there are different kinds of quantum gravity black holes, namely loop quantum black holes, noncommutative black

holes, asympotically safe black holes. In these approaches black holes are singularity free.

Fiction

• In David Brin's novel Earth a manmade micro black hole slips into the core of the earth.

• In Dan Simmons's novels Ilium and Olympos, a major landmark is "Paris Crater", the site where a man made

micro black hole's containment field failed, and the black hole sank toward the centre of the earth before

collapsing (presumably in accordance with the Hawking radiation theory), leaving a volcanic crater in its wake.

• In the short story How We Lost the Moon, A True Story by Frank W. Allen, which is actually written by Paul J.

McAuley, a micro black hole is accidentally created on the Moon and gradually consumes it.[21]

• Larry Niven's Hugo Award-winning stories The Hole Man and The Borderland of Sol deal with "quantum black

holes".

• In Martin Caidin's novel Star Bright , an object is created during an implosion-fusion test that has essentially the

properties of a micro black hole, though it is not given that name. The object is eventually destroyed, but the

resulting explosion destroys a huge area around it.

• In Steven R. Donaldson's 5 volume Gap series of books he presents singularity grenades as anti-spaceship cosmic

weapons that release a micro black hole on impact with a ship.

• In Bungie's award-winning Halo Series, spaceships travel through space by ripping the space-time continuum by

artificially generating thousands of micro black holes that quickly evaporate via Hawking radiation.

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Micro black hole 103

Notes

[1] B.J. Carr and S.B. Giddings, "Quantum black holes," Scientific American 292N5 (2005) 30. (http://www.  sciam. com/article.

cfm?id=quantum-black-holes)

[2] Giddings, S. B.; Thomas, S. D. (2002). "High-energy colliders as black hole factories: The End of short distance physics". Phys. Rev. D 65

(5): 056010. doi:10.1103/PhysRevD.65.056010. arXiv:hep-ph/0106219.

[3] Dimopoulos, S.; Landsberg, G. L. (2001). "Black Holes at the Large Hadron Collider". Phys. Rev. Lett. 87 (16): 161602.

arXiv:hep-ph/0106295.[4] Johnson, George (September 11, 2001). "Physicists Strive to Build A Black Hole" (http://www.  nytimes. com/2001/09/11/science/ 

physicists-strive-to-build-a-black-hole.html).The New York Times. . Retrieved 2010-05-12.

[5] "The case for mini black holes" (http://cerncourier. com/cws/article/cern/29199). CERN courier . Nov 2004. .

[6] Hawking, S. W. (1975). "Particle Creation by Black Holes". Commun. Math. Phys. 43 (3): 199 –220. doi:10.1007/BF02345020.

[7] Helfer, A. D. (2003). "Do black holes radiate?". Reports on Progress in Physics 66 (6): 943. doi:10.1088/0034-4885/66/6/202.

arXiv:gr-qc/0304042.

[8] Susskind, L. (2008). The Black Hole War: My battle with Stephen Hawking to make the world safe for quantum mechanics. New York: Little,

Brown. ISBN 9780316016407.

[9] Barrau, A. (2000). "Primordial black holes as a source of extremely high energy cosmic rays". Astroparticle Physics  12 (4): 269 –275.

doi:10.1016/S0927-6505(99)00103-6.

[10] McKee, M. (30 May 2006). "Satellite could open door on extra dimension" (http://www. newscientist. com/article/ 

dn9240-satellite-could-open-door-on-extra-dimension. html). New Scientist . .

[11] "Fermi Gamma Ray Space Telescope: "Mini" black hole detection" (http://fermi.  gsfc. nasa. gov/help/tech/minibh. html). .

[12] Khriplovich, I. B.; Pomeransky, A. A.; Produit, N.; Ruban, G. Yu. (2008). "Can one detect passage of small black hole through the Earth?".

 Physical Review D 77 (6): 064017. doi:10.1103/PhysRevD.77.064017.

[13] Khriplovich, I. B.; Pomeransky, A. A.; Produit, N.; Ruban, G. Yu.. "Passage of small black hole through the Earth. Is it detectable?".

 Pre-Print . arXiv:0801.4623.

[14] Cain, Fraser (20 June 2007). "Are Microscopic Black Holes Buzzing Inside the Earth?" (http://www. universetoday. com/2007/06/20/ 

are-microscopic-black-holes-buzzing-inside-the-earth).Universe Today. .

[15] The Schwarzschild radius of a 1015 grams black hole is ~148 fm (148 ? 10?15 m) (which is much smaller than an atom, but larger than an

atomic nucleus)

[16] Schewe, Phillip F.; Stein, Ben; Riordon, James (September 26, 2001). "??". Bulletin of Physics News (American Institute of Physics) 558.

[17] Choptuik, Matthew W.; Pretorius, Frans (2010). "Ultrarelativistic Particle Collisions". Phys. Rev. Lett. 104 (11): 111101.

doi:10.1103/PhysRevLett.104.111101. arXiv:0908.1780.

[18] Peng, G. X.; Wen, X. J.; Chen, Y. D. (2006). "New solutions for the color-flavor locked strangelets". Physics Letters B 633 (2 –3): 314 –318.doi:10.1016/j.physletb.2005.11.081. arXiv:hep-ph/0512112.

[19] S.B. Giddings and M.L. Mangano, "Astrophysical implications of hypothetical stable TeV-scale black holes," arXiv:0806.3381 (http:// 

arxiv. org/abs/0806. 3381), Phys. Rev. D78: 035009, 2008 (http://link.aps.org/doi/10.  1103/PhysRevD. 78. 035009)

[20] M.E. Peskin, "The end of the world at the Large Hadron Collider?" Physics 1, 14 (2008) (http://physics. aps.  org/articles/v1/14)

[21] http://www. bestsf. net/reviews/mcauleylittlemachines.html

References

• D. Page, Phys. Rev. D13 (1976) 198 (http://prola.aps. org/abstract/PRD/v13/i2/p198_1) : first detailed

studies of the evaporation mechanism

• B.J. Carr & S.W. Hawking, Mon. Not. Roy. Astron. Soc 168 (1974) 399 (http://adsabs. 

harvard. 

edu/cgi-bin/ nph-bib_query?bibcode=1974MNRAS.168.. 399C) : links between primordial black holes and the early universe

• A. Barrau et al., Astron. Astrophys. 388 (2002) 676 (http://arxiv.org/abs/astro-ph/0112486) , Astron.

Astrophys. 398 (2003) 403 (http://arxiv.  org/abs/astro-ph/0207395) , Astrophys. J. 630 (2005) 1015 (http:// 

arxiv. org/abs/astro-ph/0505436) : experimental searches for primordial black holes thanks to the emitted

antimatter

• A. Barrau & G. Boudoul, Review talk given at the International Conference on Theoretical Physics TH2002

(http://arxiv.  org/abs/astro-ph/0212225) : cosmology with primordial black holes

• A. Barrau & J. Grain, Phys. Lett. B 584 (2004) 114 (http://arxiv.org/abs/hep-ph/0311238) : searches for new

physics (quantum gravity) with primordial black holes

• P. Kanti, Int. J. Mod. Phys. A19 (2004) 4899 (http://arxiv. 

org/abs/hep-ph/0402168) : evaporating black holesand extra-dimensions

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Micro black hole 104

• D. Ida, K.-y. Oda & S.C.Park, (http://arxiv. org/abs/hep-th/0602188): determination of black hole's life and

extra-dimensions

• Sabine Hossenfelder: What Black Holes Can Teach Us, hep-ph/0412265 (http://www.arxiv.org/abs/hep-ph/ 

0412265)

• L. Modesto, PhysRevD.70.124009 (http://arxiv.org/abs/gr-qc/0407097): Disappearance of Black Hole

Singularity in Quantum Gravity

• P. Nicolini, A. Smailacic, E. Spallucci, j.physletb.2005.11.004 (http://arxiv.org/abs/gr-qc/0510112):

Noncommutative geometry inspired Schwarzschild black hole

• A. Bonanno, M. Reuter, PhysRevD.73.083005 (http://arxiv.org/abs/hep-th/0602159): Spacetime Structure of 

an Evaporating Black Hole in Quantum Gravity

External links

•  Astrophysical implications of hypothetical stable TeV-scale black holes (http://arxiv.  org/abs/0806.  3381)

• A. Barrau & J. Grain, The Case for mini black holes (http://www. cerncourier. com/main/article/44/9/22) : a

review of the searches for new physics with micro black holes possibly formed at colliders

• Mini Black Holes Might Reveal 5th Dimension (http://www.space. com/scienceastronomy/ 060626_mystery_monday. html) - Space.com

• Doomsday Machine Large Hadron Collider? (http://www.ostina.org/content/view/3547/1077/) - A scientific

essay about energies, dimensions, black holes, and the associated public attention to CERN, by Norbert Frischauf 

(also available as Podcast)

Strangelet

A strangelet is a hypothetical particle consisting of a bound state of roughly equal numbers of up, down, and strange

quarks. Its size would be a minimum of a few femtometers across (with the mass of a light nucleus). Once the sizebecomes macroscopic (on the order of meters across), such an object is usually called a quark star or "strange star"

rather than a strangelet. An equivalent description is that a strangelet is a small fragment of strange matter. The term

"strangelet" originates with E. Farhi and R. Jaffe.[1] Strangelets have been suggested as a dark matter candidate.[2]

Theoretical possibility

Strange matter hypothesis

The known particles with strange quarks are unstable because the strange quark is heavier than the up and down

quarks, so strange particles, such as the Lambda particle, which contains an up, down, and strange quark, always losetheir strangeness, by decaying via the weak interaction to lighter particles containing only up and down quarks. But

states with a larger number of quarks might not suffer from this instability. This is the "strange matter hypothesis" of 

Bodmer [3] and Witten.[2] According to this hypothesis, when a large enough number of quarks are collected

together, the lowest energy state is one which has roughly equal numbers of up, down, and strange quarks, namely a

strangelet. This stability would occur because of the Pauli exclusion principle; having three types of quarks, rather

than two as in normal nuclear matter, allows more quarks to be placed in lower energy levels.

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Relationship with nuclei

A nucleus is a collection of a large number of up and down quarks, confined into triplets (neutrons and protons).

According to the strange matter hypothesis, strangelets are more stable than nuclei, so nuclei are expected to decay

into strangelets. But this process may be extremely slow because there is a large energy barrier to overcome: as the

weak interaction starts making a nucleus into a strangelet, the first few strange quarks form strange baryons, such as

the Lambda, which are heavy. Only if many conversions occur almost simultaneously will the number of strangequarks reach the critical proportion required to achieve a lower energy state. This is very unlikely to happen, so even

if the strange matter hypothesis were correct, nuclei would never be seen to decay to strangelets because their

lifetime would be longer than the age of the universe.

Size

The stability of strangelets depends on their size. This is because of (a) surface tension at the interface between quark

matter and vacuum (which affects small strangelets more than big ones), and (b) screening of charges, which allows

small strangelets to be charged, with a neutralizing cloud of electrons/positrons around them, but requires large

strangelets, like any large piece of matter, to be electrically neutral in their interior. The charge screening distance

tends to be of the order of a few femtometers, so only the outer few femtometers of a strangelet can carry charge.[4]

The surface tension of strange matter is unknown. If it is smaller than a critical value (a few MeV per square

femtometer[5] ) then large strangelets are unstable and will tend to fission into smaller strangelets (strange stars

would still be stabilized by gravity). If it is larger than the critical value, then strangelets become more stable as they

get bigger.

Natural or artificial occurrence

Although nuclei do not decay to strangelets, there are other ways to create strangelets, so if the strange matter

hypothesis is correct there should be strangelets in the universe. There are at least three ways they might be created

in nature:• Cosmogonically, i.e., in the early universe when the QCD confinement phase transition occurred. It is possible

that strangelets were created along with the neutrons and protons which form ordinary matter.

• High energy processes. The universe is full of very high-energy particles (cosmic rays). It is possible that when

these collide with each other or with neutron stars they may provide enough energy to overcome the energy

barrier and create strangelets from nuclear matter.

• Cosmic ray impacts. In addition to head-on collisions of cosmic rays, ultra high energy cosmic rays impacting on

Earth's atmosphere may create strangelets.

These scenarios offer possibilities for observing strangelets. If there are strangelets flying around the universe, then

occasionally a strangelet should hit Earth, where it would appear as an exotic type of cosmic ray. If strangelets can

be produced in high energy collisions, then we might make them at heavy-ion colliders.

Accelerator production

At heavy ion accelerators like RHIC, nuclei are collided at relativistic speeds, creating strange and antistrange quarks

which could conceivably lead to strangelet production. The experimental signature of a strangelet would be its very

high ratio of mass to charge, which would cause its trajectory in a magnetic field to be extremely straight. The STAR

collaboration has searched for strangelets produced at the Relativistic Heavy Ion Collider, [6] but none were found.

The Large Hadron Collider (LHC) is even less likely to produce strangelets,[7] but searches are planned[8] for the

LHC ALICE detector.

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Space-based detection

The Alpha Magnetic Spectrometer (AMS), an instrument which is planned to be mounted on the International Space

Station, could detect strangelets.[9]

Possible seismic detection

In May 2002, a group of researchers at Southern Methodist University reported the possibility that strangelets mayhave been responsible for a seismic event recorded on October 22 and November 24 in 1993.[10] The authors later

retracted their claim, after finding that the clock of one of the seismic stations had a large error during the relevant

period.[11]

It has been suggested that the International Monitoring System being set up to verify the Comprehensive Nuclear

Test Ban Treaty (CTBT) may be useful as a sort of "strangelet observatory" using the entire Earth as its detector. The

IMS will be designed to detect anomalous seismic disturbances down to 1 kiloton of TNT's equivalent energy release

or less, and could be able to track strangelets passing through Earth in real time if properly exploited.

DangersIf the strange matter hypothesis is correct and a strangelet comes in contact with a lump of ordinary matter such as

Earth, it could convert the ordinary matter to strange matter.[12]  [13] This "ice-nine" disaster scenario is as follows:

one strangelet hits a nucleus, catalyzing its immediate conversion to strange matter. This liberates energy, producing

a larger, more stable strangelet, which in turn hits another nucleus, catalyzing its conversion to strange matter. In the

end, all the nuclei of all the atoms of Earth are converted, and Earth is reduced to a hot, large lump of strange matter.

This is not a concern for strangelets in cosmic rays because they are produced far from Earth and have had time to

decay to their ground state, which is predicted by most models to be positively charged, so they are electrostatically

repelled by nuclei, and would rarely merge with them.[14] [15] But high-energy collisions could produce negatively

charged strangelet states which live long enough to interact with the nuclei of ordinary matter.[16]

The danger of catalyzed conversion by strangelets produced in heavy-ion colliders has received some media

attention,[17]  [18] and concerns of this type were raised[12]  [19] at the commencement of the Relativistic Heavy Ion

Collider (RHIC) experiment at Brookhaven, which could potentially have created strangelets. A detailed analysis[13]

concluded that the RHIC collisions were comparable to ones which naturally occur as cosmic rays traverse the solar

system, so we would already have seen such a disaster if it were possible. RHIC has been operating since 2000

without incident. Similar concerns have been raised about the operation of the Large Hadron Collider (LHC) at

CERN[20] but such fears are dismissed as far-fetched by scientists.[20] [21] [22]

In the case of a neutron star, the conversion scenario seems much more plausible. A neutron star is in a sense a giant

nucleus (20 km across), held together by gravity, but it is electrically neutral and so does not electrostatically repel

strangelets. If a strangelet hit a neutron star, it could convert a small region of it, and that region would grow toconsume the entire star, creating a quark star.[23]

All the issues discussed above relating to the conversion of ordinary matter to strange matter only arise if the strange

matter hypothesis is true, and its surface tension is larger than the aforementioned critical value.

Debate about the strange matter hypothesis

The strange matter hypothesis remains unproven. No direct search for strangelets in cosmic rays or particle

accelerators has seen a strangelet (see references in earlier sections). If any of the objects we call neutron stars could

be shown to have a surface made of strange matter, this would indicate that strange matter is stable at zero pressure,

which would vindicate the strange matter hypothesis. But there is no strong evidence for strange matter surfaces on

neutron stars (see below).

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Another argument against the hypothesis is that if it were true, all neutron stars should be made of strange matter,

and otherwise none should be.[24] Even if there were only a few strange stars initially, violent events such as

collisions would soon create many strangelets flying around the universe. Because one strangelet will convert a

neutron star to strange matter, by now all neutron stars would have been converted. This argument is still debated,[25]

[26]  [27]  [28] but if it is correct then showing that one neutron star has a conventional nuclear matter crust would

disprove the strange matter hypothesis.

Because of its importance for the strange matter hypothesis, there is an ongoing effort to determine whether the

surfaces of neutron stars are made of strange matter or nuclear matter. The evidence currently favors nuclear matter.

This comes from the phenomenology of X-ray bursts, which is well-explained in terms of a nuclear matter crust,[29]

and from measurement of seismic vibrations in magnetars.[30]

In fiction

An episode of  Odyssey 5 featured an attempt to destroy the planet by intentionally creating negatively charged

strangelets in a particle accelerator.[31]

The BBC docufiction End Day features a scenario where a particle accelerator in New York City explodes, creating

a strangelet and starting a catastrophic chain reaction which destroys Earth.

The story "A Matter most Strange" in the collection  Indistinguishable from Magic by Robert L. Forward deals with

the making of strangelet in a particle accelerator.

Impact (novel), published in 2010 and written by Douglas Preston, deals with a strangelet that impacts the Earth and

Moon and passes through.

Killer Strangelets is a children's novel, written by CT Furlong and published by Inside Pocket which features a

scenario whereby a group of kids are forced to embark on a mission to CERN to stop an evil scientist, who is

involved with the Large Hadron Collider (LHC) project, from using Killer Strangelets to destroy the planet.

References

[1] E. Farhi and R. Jaffe, "Strange Matter", Phys. Rev. D30, 2379 (1984) (http://prola. aps. org/abstract/PRD/v30/i11/p2379_1)

[2] E. Witten, "Cosmic Separation Of Phases" Phys. Rev. D30, 272 (1984) (http://prola.  aps.  org/abstract/PRD/v30/i2/p272_1)

[3] A. Bodmer "Collapsed Nuclei" Phys. Rev. D4, 1601 (1971) (http://prola. aps.org/abstract/PRD/v4/i6/p1601_1)

[4] H. Heiselberg, "Screening in quark droplets", Phys. Rev. D48, 1418 (1993) (http://prola.  aps. org/abstract/PRD/v48/i3/p1418_1)

[5] M. Alford, K. Rajagopal, S. Reddy, A. Steiner, "The Stability of Strange Star Crusts and Strangelets", Phys. Rev. D73 114016 (2006)

arXiv:hep-ph/0604134 (http://arxiv.org/abs/hep-ph/0604134)

[6] STAR Collaboration, "Strangelet search at RHIC", arXiv:nucl-ex/0511047 (http://www.  arxiv. org/abs/nucl-ex/0511047)

[7] Ellis J, Giudice G, Mangano ML, Tkachev I, Wiedemann U (LHC Safety Assessment Group) (5 September 2008). " Review of the Safety of 

LHC Collisions (http://www.  iop.  org/EJ/article/0954-3899/35/11/115004/g8_11_115004.

pdf?request-id=1973667e-34da-47a4-b75a-08624558a81b)" (PDF, 586 KiB). ''Journal of Physics G: Nuclear and Particle Physics. 35,

115004 (18pp). doi:10.1088/0954-3899/35/11/115004. arXiv:0806.3414. CERN record (http://cdsweb. 

cern. 

ch/record/1111112?ln=fr).[8] A. Angelis et al., "Model of Centauro and strangelet production in heavy ion collisions", Phys. Atom. Nucl. 67:396-405 (2004)

arXiv:nucl-th/0301003 (http://arxiv.org/abs/nucl-th/0301003)

[9] J. Sandweiss, "Overview of strangelet searches and Alpha Magnetic Spectrometer: When will we stop searching?" J. Phys. G30:S51-S59

(2004) (http://www. iop. org/EJ/abstract/0954-3899/30/1/004)

[10] D. Anderson et al., "Two seismic events with the properties for the passage of strange quark matter through the earth"

arXiv:astro-ph/0205089 (http://www.arxiv.org/abs/astro-ph/0205089)

[11] E.T. Herrin et al., "Seismic Search for Strange Quark Nuggets" (http://arxiv.  org/abs/astro-ph/0505584)

[12] A. Dar, A. De Rujula, U. Heinz, "Will relativistic heavy ion colliders destroy our planet?", Phys. Lett. B470:142-148 (1999)

arXiv:hep-ph/9910471 (http://www. arxiv.org/abs/hep-ph/9910471)

[13] W. Busza, R. Jaffe, J. Sandweiss, F. Wilczek, "Review of speculative 'disaster scenarios' at RHIC", Rev. Mod. Phys.72:1125-1140 (2000)

arXiv:hep-ph/9910333 (http://www. arxiv.org/abs/hep-ph/9910333)

[14] J. Madsen, "Intermediate mass strangelets are positively charged", Phys. Rev. Lett. 85 (2000) 4687-4690 (2000) arXiv:hep-ph/0008217

(http://www.  arxiv. org/abs/hep-ph/0008217)

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[15] J. Madsen "Strangelets in Cosmic Rays", for Proceedings of 11th Marcel Grossmann Meeting, Germany, Jul 2006, arXiv:astro-ph/0612784

(http://www.  arxiv. org/abs/astro-ph/0612784)

[16] J. Schaffner-Bielich, C. Greiner, A. Diener, H. Stoecker, "Detectability of strange matter in heavy ion experiments", Phys. Rev.

C55:3038-3046 (1997), arXiv:nucl-th/9611052 (http://arxiv.org/abs/nucl-th/9611052)

[17] New Scientist, 28 August 1999: "A Black Hole Ate My Planet" (http://www.kressworks. com/Science/A_black_hole_ate_my_planet.

htm)

[18]  Horizon: End Days, an episode of the BBC television series Horizon

[19] W. Wagner, "Black holes at Brookhaven?" and reply by F. Wilzcek, Letters to the Editor, Scientific American July 1999[20] Dennis Overbye, Asking a Judge to Save the World, and Maybe a Whole Lot More, NY Times, 29 March 2008 (http://www.  nytimes. com/ 

2008/03/29/science/29collider. html?ref=us)

[21] "Safety at the LHC" (http://public. web. cern.ch/Public/en/LHC/Safety-en.html). .

[22] J. Blaizot et al., "Study of Potentially Dangerous Events During Heavy-Ion Collisions at the LHC", CERN library record (http://cdsweb.

cern. ch/search?sysno=002372601cer) CERN Yellow Reports Server (PDF) (http://doc. cern. ch/yellowrep/2003/2003-001/p1. pdf)

[23]  Astrophys. Journal  310: 261. 1986. "Strange stars" (http://adsabs.  harvard. edu/full/1986ApJ. . . 310.  . 261A).

[24] J. Friedman and R. Caldwell, "Evidence against a strange ground state for baryons", Phys. Lett. B264, 143-148 (1991)

[25] J. Madsen, "Strangelets as cosmic rays beyond the GZK-cutoff", Phys. Rev. Lett. 90:121102 (2003) arXiv:stro-ph/0211597 (http://www.

arxiv. org/abs/astro-ph/0211597)

[26] S. Balberg, "Comment on 'strangelets as cosmic rays beyond the Greisen-Zatsepin-Kuzmin cutoff'", Phys. Rev. Lett. 92:119001 (2004),

arXiv:astro-ph/0403503 (http://www.arxiv.org/abs/astro-ph/0403503)

[27] J. Madsen, "Reply to Comment on Strangelets as Cosmic Rays beyond the Greisen-Zatsepin-Kuzmin Cutoff", Phys. Rev.Lett. 92:119002(2004), arXiv:astro-ph/0403515 (http://www.arxiv. org/abs/astro-ph/0403515)

[28] J. Madsen, "Strangelet propagation and cosmic ray flux",Phys. Rev. D71, 014026 (2005) arXiv:astro-ph/0411538 (http://www.  arxiv. org/ 

abs/astro-ph/0411538)

[29] A. Heger, A. Cumming, D. Galloway, S. Woosley, "Models of Type I X-ray Bursts from GS 1826-24: A Probe of rp-Process Hydrogen

Burning", arXiv:0711.1195 (http://arxiv.  org/abs/0711.1195)

[30] A. Watts and S. Reddy, "Magnetar oscillations pose challenges for strange stars", MNRAS, 379, L63 (2007) arXiv:astro-ph/0609364 (http:/ 

 /arxiv.  org/abs/astro-ph/0609364)

[31] Odyssey 5: Trouble with Harry (http://www.  imdb.com/title/tt0664394/), an episode of the Canadian science fiction television series

Odyssey 5 by Manny Coto (2002)

Further reading

• Holden, Joshua (May 17, 1998). "The Story of Strangelets" (http://www. physics. rutgers.edu/~jholden/ 

strange/strange. html). Rutgers. Retrieved 2010-04-01.

• Fridolin Weber (2004). "Strange Quark Matter and Compact Stars". arΧiv:astro-ph/0407155 [astro-ph].

• Jes Madsen (1998). "Physics and Astrophysics of Strange Quark Matter". arΧiv:astro-ph/9809032 [astro-ph].

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109

Future

Super Large Hadron ColliderIntersecting Storage Rings CERN, 1971 –1984

Super Proton Synchrotron CERN, 1981 –1984

ISABELLE BNL, cancelled in 1983

Tevatron Fermilab, 1987 –present

Relativistic Heavy Ion Collider BNL, 2000 –present

Superconducting Super Collider Cancelled in 1993

Large Hadron Collider CERN, 2009 –presentSuper Large Hadron Collider Proposed, CERN, 2019 –

Very Large Hadron Collider Theoretical

The Super Large Hadron Collider (SLHC) is a proposed upgrade to the Large Hadron Collider to be made after

around ten years of operation. The upgrade aims at increasing the luminosity of the machine by a factor of 10, up to

1035cm−2s−1, providing a better chance to see rare processes and improving statistically marginal measurements.

Many different paths exist for upgrading the collider. A collection of different designs of the high luminosity

interaction regions is being maintained by the European Organization for Nuclear Research (CERN). [1] A workshop

was held in 2006 to establish which are the most promising options.[2] A comprehensive press article on this

workshop can be found at the CERN Courier [3]. A summary of the possible machine parameters can be found atMachine parameters collection [4].

Increasing LHC luminosity involves reduction of beam size at the collision point and either reduction of bunch

length and spacing, or significant increase in bunch length and population. The maximum integrated luminosity

increase of the existing options is about a factor of 4 higher than the LHC ultimate performance, unfortunately far

below the LHC upgrade project's initial ambition of a factor of 10. However, at the latest LUMI'06 workshop, [2]

several suggestions were proposed that would boost the LHC peak luminosity by a factor of 10 beyond nominal

towards 1035 cm−2s−1.

The resultant higher event rate poses important challenges for the particle detectors located in the collision areas.[5]

Injector upgrade

As part of the Phase 2 Super LHC, significant changes would be made to the proton injector.

Superconducting Proton Linac (SPL): Accelerating protons with superconducting radio frequency cavities to an

energy of 5GeV.

Proton Synchrotron 2 (PS2): Accelerating the beam from 5GeV at injection to 50GeV at extraction.

Super Proton Synchroton (SPS) Upgraded: The present SPS would be substantially upgraded to handle in increased

beam intensity from PS2.

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Super Large Hadron Collider 110

References

[1] IR optics collection (http://care-hhh.web. cern. ch/care-hhh/SuperLHC_IRoptics/IRoptics. html)

[2] LUMI 06 workshop (http://care-hhh.web. cern. ch/CARE-HHH/LUMI-06/default. html)

[3] http://cerncourier. com/cws/article/cern/29838

[4] http://care-hhh. web. cern. ch/CARE-HHH/LUMI-06/lhcupgradeparameters.htm

[5] ATLAS upgrade web page (http://atlas.web.cern. ch/Atlas/GROUPS/UPGRADES/)

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Very Large Hadron Collider 111

Very Large Hadron Collider

Intersecting Storage Rings CERN, 1971 –1984

Super Proton Synchrotron CERN, 1981 –1984

ISABELLE BNL, cancelled in 1983

Tevatron Fermilab, 1987 –present

Relativistic Heavy Ion Collider BNL, 2000 –present

Superconducting Super Collider Cancelled in 1993

Large Hadron Collider CERN, 2009 –present

Super Large Hadron Collider Proposed, CERN, 2019 –

Very Large Hadron Collider Theoretical

The Very Large Hadron Collider (VLHC) is a name for a hypothetical future hadron collider with performance

significantly beyond the Large Hadron Collider.[1]

There is no planned location or schedule for the VLHC; the name is used only to discuss the technological feasibility

of such a collider and ways that it might be designed.

Given that such a performance increase necessitates a correspondingly large increase in size, cost, and power

requirements, a significant amount of international collaboration over a period of decades would be required to

construct such a collider.

See also

• Particle physics

References

[1] Glanz, James (2001-07-10). "Physicists Unite, Sort of, on Next Collider" (http://www.  nytimes. com/2001/07/10/science/ 

physicists-unite-sort-of-on-next-collider. html). The New York Times. . Retrieved 2009-06-27.

External links

• vlhc.org (http://vlhc. org/), a Fermilab webpage on VLHC research and development

• VLHC Design Materials (http://tdserver1.fnal.gov/tddoc/DesignStudyReport/)

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Wwheaton, XJamRastafire, XP1, Xasdas, Xertoz, YUL89YYZ, Yamamoto Ichiro, Yellowdesk, Yhkhoo, Ylai, Yuefairchild, ZZ9pluralZalpha, Zaak, Zargulon, Zimbabweed, Zomglolwtfzor,Zonk43, Zsinj, Ztbbq, Ztobor, Zykure, Zythe, 1421 anonymous edits

List of LHC experiments  Source: http://en.wikipedia.org/w/index.php?oldid=359030335 Contributors: Auntof6, Headbomb, Ironholds, Rursus, Tetrflare, Xezbeth, 5 anonymous edits

ALICE  Source: http://en.wikipedia.org/w/index.php?oldid=380523181 Contributors: Andrius.v, Caiyu, Connor Behan, Dsupriya, Econ oh my, Edgar181, Erik J, Erwinrossen, Franznavach,Harp, Headbomb, Javachan, Khukri, Kyurkewicz, Laurascudder, LeoNomis, Madhero88, MagdaGa, Meno25, Merrybrit, Mnmngb, One, RafaAzevedo, Rich Farmbrough, SCZenz, Seneka,Sensenmann, Tainels, Tide rolls, Xinebbsa, Мыша, 55 anonymous edits

ATLAS  Source: http://en.wikipedia.org/w/index.php?oldid=388673677 Contributors: 84user, AB, AcademyAD, Akamad, Amapelli, AndrewWatt, Andrius.v, Apis O-tang, Bcrowell,Bobblewik, Bovineone, Bridgeplayer, Bunchofgrapes, Bzzybee13, Charles Matthews, Ciphers, Col. Hauler, Cowman109, Curps, Cyberia23, Cynicism addict, Davdde, Djinn65,

DragonflySixtyseven, Ehn, Erkcan, Flying fish, Francphy5, Francs2000, Freakofnurture, Frencheigh, GangofOne, Gene Nygaard, Gregb, Gurch, Harp, Harryboyles, Headbomb, Herr apa, IdaShaw, Jag123, Jmnbatista, Joopercoopers, Juhanson, Khukri, Kozuch, Kyurkewicz, Laurascudder, LeoNomis, Linas, Loodog, Lumidek, Lupin, MagdaGa, Mako098765, Mallorn, Mandavi,Manfalk, Martijn Hoekstra, Master z0b, Matt Crypto, Maxkramer, Mets501, Mithridates, Mjaekel, Neparis, O. Harris, Orion11M87, Pediadeep, PeterMcCready, Plasticup, Rama, RichFarmbrough, Rjwilmsi, Rob.derosa, SCZenz, SandyGeorgia, Sdedeo, Sfdan, Sheliak, SimonP, SinWin, Spellmaster, Splash, Ssayler, Suruena, Susvolans, The wub, Tony1, Tushar.bhatnagar, V9,Vald, WISo, Wayward, Wiki alf, Woodrowr, Z6, Zondor, 120 anonymous edits

CMS  Source: http://en.wikipedia.org/w/index.php?oldid=389077931 Contributors: Angelastic, Beno1000, Besselfunctions, Bkell, Bornerdogge, Chandrasonic, Chronitis, Cougarsoul, Dirc,Erkcan, Everyme, Falcorian, GeeJo, Gene Nygaard, Harp, Headbomb, Herbee, Icalanise, Isnow, JabberWok, Jimbrooke, Jll, Jz 007, Khukri, Kyurkewicz, Laurascudder, LeoNomis, LokiClock,LorenzoB, MagdaGa, MartinGrunewald, Michael Hardy, Mnmngb, Murielvd, Netrapt, Nevit, Nonnormalizable, Ojs, Pizza1512, Qking, Rama, Reality3chick, Rich Farmbrough, Rjwilmsi,SchmittM, Sheliak, Slashme, Slathering, Spellage, Suruena, Techieb0y, Tiki2099, Tkolberg, Topperfalkon, TriTertButoxy, WISo, Zarniwoot, Δζ, 81 anonymous edits

LHCb  Source: http://en.wikipedia.org/w/index.php?oldid=389487070 Contributors: A1056207, AndyBuckley, Barry m, Conscious, DJIndica, Davdde, GraemeL, Harp, Headbomb, KeenanPepper, Khukri, Kyurkewicz, Larosch, Laurascudder, LeoNomis, Linas, Mark Williamson, Minimac, Nick, Oswald le fort, Pip2andahalf, Pkoppenb, Remuel, Rich Farmbrough, Ryan Roos,SCZenz, Sheliak, Spike Wilbury, Steve Quinn, Themisb, Turnstep, WISo, 27 anonymous edits

LHCf   Source: http://en.wikipedia.org/w/index.php?oldid=353282917 Contributors: Alby, Alessia2703, Alynna Kasmira, Bobo192, CaptinJohn, Davdde, Erkcan, Headbomb, Javachan, Khukri,Kyurkewicz, Laurascudder, LeoNomis, Orion11M87, Puzl bustr, Rich Farmbrough, Sheliak, 11 anonymous edits

FP420  Source: http://en.wikipedia.org/w/index.php?oldid=353524901 Contributors: Headbomb, Jakkinx, Rettetast, Slyatslys, Thomas Blomberg

TOTEM  Source: http://en.wikipedia.org/w/index.php?oldid=388666339 Contributors: 7segment, Adrian 1111, Conscious, Francoroldan, Gortu, Harp, Headbomb, Javachan, Jcw69, Kaspar.jan,Khukri, Kyurkewicz, Laurascudder, LeoNomis, Philopp, Rapsar, Rich Farmbrough, Sheliak, 12 anonymous edits

LHC Computing Grid  Source: http://en.wikipedia.org/w/index.php?oldid=378876848 Contributors: Beland, Bender235, BillinSanDiego, Bobbias, Cgingold, Chrishomingtang, Cobaltbluetony,Egil, Eleveneleven, Ethyr, Fifieldt, GregorB, Headbomb, IG-64, JMacalinao, Jbond00747, JukoFF, Kolbasz, Legosock, Lightmouse, Mattgirling, Pakaraki, Randysnow, Sim@simpol.net,Superm401, Twigboy, Walkingstick3, 33 anonymous edits

LHC@home  Source: http://en.wikipedia.org/w/index.php?oldid=354069016 Contributors: .snoopy., 100110100, Bender235, Beno1000, Beyazid, Bovineone, Bruce89, Cgingold, Creidieki,Dirk P Broer, Echoray, Erkcan, Eyreland, FayssalF, Gamer007, GeneralBelly, Giftlite, Headbomb, Hellcat fighter, Hex87, Ilyanep, Jjhat1, Justice Marshall, Kinhull, Laurascudder, LeoNomis,Lzur, Maurice Carbonaro, Minghong, Mr. Billion, Noderaser, Nucleusboy, PrimeHunter, Professorolous, Pstanton, Rich Farmbrough, RoyBoy, SCZenz, The CISer, Valodzka, Wdfarmer,Wikiacc, Wwoods, Ysangkok, ZeroOne, 13 anonymous edits

Proton Synchrotron Booster  Source: http://en.wikipedia.org/w/index.php?oldid=353617189 Contributors: Andrius.v, Buddy431, Eshmo, Headbomb, Khukri, Laurascudder, Rtomas, Sheliak, 4anonymous edits

VELO  Source: http://en.wikipedia.org/w/index.php?oldid=357996895 Contributors: Bhadani, Headbomb, Larosch, Madcoverboy, Malcolma, Nateji77, Passportguy, Themisb

Standard Model  Source: http://en.wikipedia.org/w/index.php?oldid=389696646 Contributors: A. di M., APH, Addshore, Afteread, Agasicles, Agasides, Alan Liefting, Alansohn, Alinor,Aliotra, Alison, AmarChandra, Andre Engels, AnonMoos, Aoosten, Arivero, AugPi, Awren, AxelBoldt, Axl, Bakken, Bambaiah, Bamkin, Barak Sh, Bassbonerocks, BenRG, Benbest,Bender235, Beta Orionis, Bevo, Bodhitha, Bookalign, Bovineone, Brews ohare, Brim, Brockert, Bryan Derksen, Bubba73, Bytbox, C0nanPayne, CYD, Caco de vidro, CattleGirl, Chris the

speller, ChristopherWillis, Complexica, Craig Bolon, Crazz bug 5, Crum375, D-Notice, DWHalliday, Daniel.Cardenas, DannyWilde, Dauto, Dave1g, David Barnard, David Schaich, Davidspector, Dbenbenn, Dbraize, Deepmath, DerNeedle, Derek Ross, Dextrose, Dfan, Diagramma Della Verita, Djr32, Dmmaus, Dratman, Drhex, Drrngrvy, Dstudent, Dv82matt, Dysepsion, Edsegal,Eeekster, Egg, Ekjon Lok, El C, Elsweyn, Epbr123, Ernsts, Escalona, FT2, Faethon, Faethon34, Faethon36, Fences and windows, Fogger, FrankTobia, Gary King, Gatortpk, Geremia, Giftlite,Glenn, Gnixon, Goop Goop, Goudzovski, Gparker, Gscshoyru, Guarracino, Guy Harris, H2g2bob, HEL, Hal peridol, Haoherb428, Harp, Harrigan, Headbomb, Herbee, Hexane2000, Hirak 99,HorsePunchKid, HungarianBarbarian, Icairns, Icalanise, Iomesus, Isis, Itinerant1, J Milburn, J.delanoy, JLaTondre, JabberWok, Jacksonwalters, Jagged 85, JamesAM, JarahE, JeffBobFrank,Jeffq, Jeodesic, Jessemv, Jgwacker, Jmnbatista, Joshmt, Jrf, Jrtayloriv, Jrw@pobox.com, JulesH, Julesd, Kacser, Kate, KathrynLybarger, Kenmint, Kocio, Laurascudder, LeYaYa, Len Raymond,Leszek Jańczuk, Likebox, LilHelpa, Linas, Lomn, Looxix, Lottamiata, Macumba, Maldmac, Melchoir, Metacomet, Michael C Price, Michael Hardy, Michaelbusch, Mindmatrix, Mjamja,Monedula, Moose-32, Mosaffa, MovGP0, Mpatel, Mxn, Naraht, Nozzer42, Ohwilleke, Ordovico, Orion11M87, Orionus, Patrick, Pharotic, Phr, Phys, Physicist brazuca, Physics therapist,Populus, QFT, QMarion II, Qwertyca, R.e.b., RG2, Ram-Man, Rama, Raven in Orbit, Rbj, Reddi, Rjwilmsi, Rmrfstar, Roadrunner, Robdunst, Roscoe x, SCZenz, Schucker, SebastianHelm,Securiger, Setanta747 (locked), Setreset, SheepNotGoats, Sheliak, Silly rabbit, Sligocki, Soarhead77, Sonjaaa, Stannered, Steve Quinn, Stevertigo, Stillnotelf, Superm401, Superwj5, Swamy g,TPickup, Tanner Swett, Tarcieri, Tariqhada, Template namespace initialisation script, TenOfAllTrades, Tetracube, Texture, That Guy, From That Show!, The Anome, The Transliterator,Thunderboltz, Tom Lougheed, TriTertButoxy, Truthnlove, Twas Now, UniversumExNihilo, Van helsing, Verdy p, Vessels42, Voorlandt, VoxMoose, WJBscribe, Waggers, Wilhelm-physiker,Wwheaton, Xerxes314, Xezbeth, YellowMonkey, Yevgeny Kats, Youandme, 292 anonymous edits

Particle physics  Source: http://en.wikipedia.org/w/index.php?oldid=388883848 Contributors: 128.12.93.xxx, 142.58.249.xxx, 64.26.98.xxx, APH, Agerom, Ahoerstemeier, Allstarecho,Almostcrime, AndreasJS, Archer7, Arekku, Ark, Aroodman, Arthena, Atlant, Austin Maxwell, Awmarcz, AxelBoldt, Bambaiah, Bamkin, Barbara Shack, Battlemage, Bdesham, Bennylin, Bevo,Bggoldie, Bm gub, BobertWABC, Bobo192, Bodhitha, Boing! said Zebedee, Boud, Brandonlovescrashincastles, Brews ohare, BurtPeck, CRGreathouse, CRKingston, CWii, CYD, Calmypal,Caltas, CambridgeBayWeather, Can't sleep, clown will eat me, Celithemis, Ch2pgj, Chenyu, Cjc38, CloudNineAC, Complex (de), Comrade42, Conversion script, Csgwon, Cybercobra, DHN,DV8 2XL, Dauto, Deglr6328, Dev 176, Diligent Terrier, Discospinster, Djegan, Docu, Dominick, Donarreiskoffer, Donzzz77, Edward Z. Yang, El C, El Snubbe, Ellywa, Eloquence, EmanCunha,Emijrp, Eog1916, Erwinrossen, FT2, Falcon8765, Falconkhe, Fieldday-sunday, Fruge, Gaius Cornelius, Gareth Owen, Gary King, Gbrandt, GeorgeLouis, Ghalhud, Giftlite, Glenn, Gnixon,Gnomon Kelemen, Goodnightmush, Goudzovski, Graham87, Hdeasy, Head, Headbomb, Hectorthebat, Henry W. Schmitt, Hfastedge, Howdychicken, Howie Goodell, Ilmari Karonen, Immunize,Inwind, Iridescent, Isnow, Ixfd64, J.delanoy, JRR Trollkien, JaGa, Jagged 85, Jameskeates, Jamesontai, JamieS93, Jgwacker, JimVC3, Jimbill4321, Joe N, Joe iNsecure, Jomoal99, JonasRH,Joshmt, Jpowell, Jung dalglish, Jxzj, Kakofonous, Karol Langner, Kenneth M Burke, Kocio, Korath, Kozuch, Kuru, Kurzon, LX, Langsytank, Larry Sanger, Laussy, Le sacre, Lee Daniel Crocker,Lightdarkness, Lightmouse, Ling.Nut, Looxix, Lor772, Lseixas, Lumidek, Lupin, MER-C, MK8, Mako098765, Marcus Qwertyus, Master Jay, Matt Crypto, Matt Gies, Matthew Woodcraft,Mattmartin, Maurreen, Mav, Mayumashu, Mcneile, Md7t, Melchoir, Mermaid from the Baltic Sea, Metrictensor, Mets501, Michael Hardy, MichaelMaggs, Micraboy, Mignon, Mike2vil,MoogleEXE, Mouse7525, Mpatel, Mullactalk, Munkay, Mxn, NellieBly, News0969, Novacatz, NuclearWinner, Ohwilleke, Oldnoah, Olexandr Kravchuk, OpenToppedBus, Orion11M87,Orpheus, Oxymoron83, Palfrey, Pandacomics, Party, Patrick, Pcd72, Pchapman47879, Penarestel, Pet3r, PhySusie, Phys, Physics, Physicsdavid, Physis, Planlips, Plastadity, Poopfacer,PranksterTurtle, QFT, RE, Ragesoss, Raphtee, Raul654, Ravi12346, Redvers, Res2216firestar, Rholton, Rich Farmbrough, Rje, Rl, Roadrunner, Rorro, Ryan Postlethwaite, SCZenz,Saeed.Veradi, SaltyBoatr, Sanders muc, Savidan, ScienceApologist, Scottfisher, Selkem, Shawn in Montreal, Silly rabbit, SimonMayer, SimonP, Sjakkalle, Smarcus, Snigbrook, Sodium,Someguy1221, Srleffler, Stephenb, Steve Quinn, SwordSmurf, TallMagic, Techraj, The Epopt, Tpbradbury, Trecool12, Trelvis, Truthnlove, Tycho, UncleDouggie, UninvitedCompany, Urvabara,Van helsing, VictorFlaushenstein, Vishnava, Voidxor, Voyajer, Wavelength, Who, Witguiota, XJamRastafire, Ylai, Zanzerjewel, Ъыь, 367 anonymous edits

Superpartner  Source: http://en.wikipedia.org/w/index.php?oldid=384571760 Contributors: Alai, Antixt, Barak Sh, Bobathon71, Carlog3, Conscious, Donarreiskoffer, Drrngrvy, Duncan.france,Giftlite, Headbomb, Jgwacker, Kocio, LovroZitnik, Madacs, Maliz, Mpatel, Phys, R.e.b., Reedy, Roadrunner, SCZenz, SimonP, SkyLined, 5 anonymous edits

Supersymmetry  Source: http://en.wikipedia.org/w/index.php?oldid=386727850 Contributors: Acjohnson55, Ancheta Wis, Andre Engels, Anville, Arivero, Barak Sh, BenRG, Blaxthos, Bodera,Bryan Derksen, C9, CES1596, Cadmasteradam, Can't sleep, clown will eat me, Cgingold, Chaos, Charles Matthews, Charleswestbrook, Chessmaster7m, Cless Alvein, Closedmouth, Complexica,Crum375, Cuboidal, DO'Neil, Dan Gluck, Ddimensões, Deglr6328, Drrngrvy, Duk, Eddie Nixon, El C, Epolk, F Notebook, Ferkelparade, Francescog, Fropuff, Gagoga ju, Gary King, Giftlite,

Gil987, Girl Scout cookie, Gparker, Gsard, Gus Polly, HaloStereo1, Headbomb, IMSoP, J.christianson, JarahE, Jcpilman, Jeandré du Toit, Jgwacker, Jordan14, Josiah Rowe, Jpod2,Kawakameha, Kborland, Kevin Hickerson, Killing Vector, Koeplinger, Kostisl, Kurochka, Lambiam, LiDaobing, LostLeviathan, Lumidek, MFH, Maarten van Vliet, Maliz, Maury Markowitz,Maxim Razin, Maximus Rex, Mdanziger, Mgnbar, Michael C Price, Michael Hardy, Mira, Mishas42, Monedula, Mor, Moyogo, Mpatel, Mporter, Nn123645, Nonnormalizable, Nowhither,Ohwilleke, Pearle, Pharotic, Phys, PhysPhD, Plumpurple, Ptrslv72, Puzl bustr, QFT, R.e.b., RG2, RJFJR, Radagast83, Raul654, Reaverdrop, Rich Farmbrough, Rjwilmsi, Roadrunner, Robma,

8/8/2019 hadron collider

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Article Sources and Contributors 114

Roybb95, Rursus, Salgueiro, Sam Hocevar, Scrabby, SeventyThree, Sheliak, Smack, Solarapex, Stevertigo, Susy is it, Taw, Ted BJ, That Guy, From That Show!, TheMaster42, Theresa knott,TimothyRias, Tktktk, TriTertButoxy, Tweet Tweet, Unconcerned, VermillionBird, Wangjiaji, Wavelength, WikHead, Wtmitchell, Xerxes314, Xiaphias, Yevgeny Kats, Zahd, Zentropa77, 163anonymous edits

Higgs boson  Source: http://en.wikipedia.org/w/index.php?oldid=389130570 Contributors: -dennis-, 1ForTheMoney, A Man In Black, A. di M., ABF, Aardvark23, Abdullais4u, Adrideba,Alansohn, Allstarecho, Altenmann, Alyjack, AnOddName, Anaxial, AndersFeder, AndrewN, Andrius.v, Angelo souti, AnonMoos, Anonymi, Antixt, Archelon, Art LaPella, Artur80, Asmeurer,Atomicthumbs, AxelBoldt, Baad, Bambaiah, Bbbl67, Bcody80, Bcorr, BenRG, Bender235, Benplowman, Betterusername, Bevo, Big Brother 1984, Biker Biker, Bjankuloski06en, BobertWABC,Bodhitha, Bookofjude, Boson15, Brian Fenton, Brians, Bryan Derksen, Bubba73, BullRangifer, C S, CYD, Cadmasteradam, Caknuck, Calmer Waters, CamB424, CamB4242, CesarB, Cgd8d,Cgwaldman, CharlesC, Chetvorno, Chreod, ChrisO, Christopher Thomas, Chuckupd, Cinkcool, Closedmouth, Consumed Crustacean, CrazyInSane, Cructacean, D'Agosta, DBGustavson,DKqwerty, DMurphy, Daniel C, DannyDaWriter, Dante Alighieri, Dauto, Dave3457, David spector, Dbachmann, DeadlyMETAL, Deceglie, Dekker451, Dirkbb, Discospinster, Diza,Donarreiskoffer, DrGaellon, Dragon of the Pants, Dratman, Drmies, DÅ‚ugosz, EchetusXe, Ehn, Eikern, El C, ElfQrin, Eliga, Endersdouble, Epastore, Er ouz, Eritain, Ernsts, Excirial, Fatram,

Fiziker, Fleisher, Fleminra, Flyguy649, Foobar, Foober, Foonle77, Fotoni, Frglee, Frymaster, Fæ, GDallimore, Gaurav, Giandrea, Giftlite, Gil987, Gobbledygeek, Goethean, Golbez, Goudzovski,GregorB, Gurch, Gwib, Hadal, Hairy Dude, Harold f, Harp, Headbomb, Hellbus, Herbee, Heron, Higgshunter, Hippypink, Icairns, Iknowyourider, Ilmari Karonen, Impunv, Infestor, Irenan,Itinerant, Itinerant1, Iwpg, J M Rice, J mcandrews, J.delanoy, JCSantos, JTiago, JabberWok, Jacques Antoine, JasonAQuest, Jc odcsmf, Jde123, Jdigitalbath, Jehochman, Jezzabr, Jfromcanada,Jgwacker, Jimtpat, Jkl, JohnArmagh, Johnflux, Jomoal99, JonathanDP81, Jonburchel, Jor63, Joriki, JorisvS, Josh Cherry, Jpod2, Jtuggle, Justinrossetti, KHamsun, Kaihsu, KapilTagore,Kbdank71, Kbk, Kborland, Keith-264, Kencf0618, Kendrick7, Kenneth Dawson, Kgf0, Koavf, Kocio, Konor org, Kooo, Krioni, Kyng, La goutte de pluie, Lambiam, Laplacian, Laurascudder,Lee M, Lethe, Lewisxxxusa, LilHelpa, Linas, Loves martyr, Lycurgus, M-Falcon, Mani1, Manning Bartlett, Marcel Kosko, Marcus Brute, Markdavid2000, Martaf, Martijn Hoekstra,Martinthoegersen, Mary at CERN, Maryhit, Master1228, Masterofpsi, Matan568, McSly, McVities, Mcorazao, Meier99, Melchoir, Meldor, Merovingian, Mesons, Mgimpel, Michael C Price,Mike Peel, Mindmatrix, Minimac, Moeron, Moose-32, Mukadderat, Mx3, Mxn, My76Strat, N4tur4le, Nafhan, NawlinWiki, NeilN, Netrapt, NeverWorker, Newone, Newzebras, Nightscream,Nihiltres, NikiAnna, Nimur, Nobleacuff, Nondisclosure, Norm mit, Northumbrian, Norvy, Novemberrain94, Now dance, fu.cker, dance!, Nsbinsnj, Nskillen, Nurg, Nuujinn, Oddz, Ohnoitsjamie,Onesius, Opkdx, Oreo Priest, Orionus, Owain, Pagw, Paine Ellsworth, PeterTheWall, Peterbullockismyname, Phil Boswell, Philip Trueman, Photonh2o, Phys, PhysicsGrad2013, Pie4all88,Pip2andahalf, Pizza1512, Praveen pillay, ProjeX, Proofreader77, Pulickkal, Quadell, Quasipalm, Quatschman, Qutezuce, R.e.b., Rangelov, Raoul NK, Reinoutr, Resonance cascade,RetiredUser2, Reuben, RevenDS, Rich Farmbrough, Rick7425, Rjwilmsi, Roadrunner, RobertG, Roman à clef, Rotiro, Rursus, Ruslik0, SCZenz, Safety Cap, Salsb, Sasquatch, Sbove, Sburke,ScAvenger, Schucker, Selva, ShaneCavanaugh, Shawn@garbett.org, Shimgray, Shirifan, Sjdunn9, Slawojarek, Sligocki, Spemble, Splarka, SqueakBox, Srleffler, StAnselm, StaticGull, SteveQuinn, StevenVerstoep, Strait, Superm401, Tburket, Tbushman, Tdent, TeunSpaans, Tevatron, The Original Wildbear, The Thing That Should Not Be, TheBendster, Thor Waldsen, Three887,Thruston, Tide rolls, Tigga en, Tim Shuba, Tom12519, TotoBaggins, Tpbradbury, TriTertButoxy, Tritium6, Twas Now, Universalsuffrage, Usp, V1adis1av, Varlaam, WAS 4.250, WLU, Waldir,Weaselpit, WikiUserPedia, Wikiborg, Wmlschlotterer, Wnt, Xerxes314, Yevgeny Kats, Ylee, Yoweigh, Zekemurdock, Zentropa, 511 anonymous edits

Safety of particle collisions at the Large Hadron Collider  Source: http://en.wikipedia.org/w/index.php?oldid=386684822 Contributors: 2over0, Ageekgal, Alansohn, Alexius08,Allemandtando, Andrew Nutter, Annoyed with fanboys, Apalsola, Apparition11, Artichoker, Atkinson 291, Ayrton Prost, B7T, BCEagle21, Barak Sh, Baronnet, BenRG, Blehfu, Blueknightex,Bobo192, Boccobrock, BoogieRock, Bovineone, Bytbox, Canberra User, Cgingold, Chovain, Closedmouth, Cmpd1, Colonel Warden, ConspiracyFAIL, Conte0, Contribut, Cybercobra,DannyDaWriter, Darkensei, Darkoneko, Darrenhusted, Davidbeaumont, Dayewalker, Dferg, Dkasak, Dr.K., Dustand, Eaefremov, Eeekster, Elonka, Emmalouise99, Excirial, FeanorStar7,Feedahungryhippo, Fetchcomms, Fieldday-sunday, Fred Stober, Frostlion, Furrykef, Gazimoff, General Epitaph, GregorB, HaeB, Headbomb, Hqb, HumanJHawkins, Ilikefood, Ilmari Karonen,IngerAlHaosului, Islander, J.delanoy, Jalabi99, James Frankcom, Jamie C, Jeffq, Jehochman, John Nevard, Johnson Lau, Jonathan Drain, Jtankers, Jtrainor, Jwoodger, Kevin, Khukri, Koavf, Lfh,MMS2013, Mandarax, MarkTB, Maxime.Debosschere, Mcorazao, MickMacNee, Milesgillham, Million Moments, Miquonranger03, Mmerlo, Moondyne, NerdyNSK, Newone, Oldnoah,Orbnauticus, Orion11M87, Ormers, Patfrank, Perardi, Phenylalanine, PhySusie, Physchim62, Plasticup, Profgregory, Psychlohexane, Ptrslv72, RKT, Radical Mallard, RainbowOfLight, Rorro,SCZenz, SaveTheWhales, ScienceApologist, SheffieldSteel, Sizif, Smith609, SoSaysChappy, Sockatume, Sophus Bie, Sparrowgoose, SqueakBox, Stabby Joe, Staka, Steve Smith,Stevenfruitsmaak, Stevenj, Strait, Strayan, Swagmuncher, THEemu, Th1rt3en, The Anome, TheBilly, TheDoober, Thumperward, TimothyRias, Tombomp, TrevorX, Verbal, Vyznev Xnebara,Woohookitty, Wwheaton, XXOni-kunXx, Yar Kramer, Yellowdesk, 170 anonymous edits

Micro black hole  Source: http://en.wikipedia.org/w/index.php?oldid=381339222 Contributors: Againme, Aisphording, Antaeus Feldspar, Antixt, ArmAndLeg, Aswarp, Auric,BalanceRestored, Bender235, Bento00, Berndf, Blanchardb, Blue Tie, Bobwhitten, BradBeattie, Caco de vidro, Cacycle, Cam-Ann, Capricorn42, Chovain, Chris the speller, Christopher Thomas,Clarityfiend, Clark89, CrankyScorpion, Crunchy Numbers, D, Danielgrad, Deamon138, DeathNomad, Deb, Deconstructhis, Delldot, Discospinster, Diverman, DonJStevens, Donald Albury,Draugen, Dreadstar, EdC, Eequor, Egil, Ehn, El C, Ersik, Esorbalo, FF2010, Fairandbalanced, FineCheeses, Fkara, Fleela, Giftlite, GraemeL, Gravitivistically, GregorB, Headbomb, Hellbus,Henrygb, IVAN3MAN, Iluvcapra, Ixfd64, JForget, Jack Merridew, Jamesontai, Jeff G., Jennavecia, Jheald, Jheise, Katieh5584, Khukri, Lainagier, Lenticel, Lethesl, Light current, Linas,Lysdexia, Mandarax, Martin-C, Mazarin07, Mckaysalisbury, Meelar, Melamed katz, Natecull, NonvocalScream, Norbi et Orbi, Nsaa, Numbo3, Oerjan, Olau, Oldnoah, Oni Lukos, Opie, Otus,Palpatine, Patrick, Paxfeline, Phenylalanine, Philip Trueman, Physprof, Pjf, Profgregory, Quasarq, Qxz, RBM 72, Radical Mallard, RayBirks, Rmrfstar, Roadrunner, Ronhjones, SJP, Scepia,Scootey, Scpark, Siener, Silverhill, Sinus, Skunkboy74, Smithbrenon, Snowolf, Spiralx, Supersheep, Sverdrup, Tarotcards, Teehee123, The Thing That Should Not Be, Thiseye, Timwi, Trilobite,

Trilobitealive, Uiteoi, Utan Vax, V1adis1av, Vanisheduser12345, Velho, Vinsfan368, Viriditas, Wesino, Wiki alf, WikiFew, WurmWoode, XJamRastafire, Yettie0711, Zeimusu, , 182anonymous editsدمحأ

Strangelet  Source: http://en.wikipedia.org/w/index.php?oldid=390250394 Contributors: 3vil-Lyn, Army1987, Barak Sh, Barry Haworth, Brad Rousse, CharacterZero, Chkno, Chouca, Chovain,Christopher Thomas, Cybercobra, Danielgrad, Dark Formal, Dark Shikari, Darksun, Davidhorman, Demophon, Dmitry Brant, DomQ, Edvvc, Eyu100, Fourohfour, Gerasime, Gunark, Headbomb,Henry the 1st, Homocion, Hydraton31, Il Sc0rpi0ne, Insidepocket, It Is Me Here, Jackol, JarahE, Johann137, Johnthescavenger, Joquarky, Julesd, Justacec, Kgf0, Killing Vector, KungFuMonkey,Lainagier, Lethesl, Light current, LokiClock, Maxime.Debosschere, Mjamja, MoeDrippins, NawlinWiki, Nfwu, NightmareZ, Nihiltres, OS2Warp, OlEnglish, Oldnoah, Oliver Pereira, OrangeSuede Sofa, Oxymoron83, Pauli133, Petero9, Pgan002, Phenylalanine, Physchim62, PsychoJosh, Radical Mallard, Retodon8, Rich Farmbrough, Rickythesk8r, Robert Treat, Someguy1221,Specious, Squideshi, Suslindisambiguator, Takeshi Nakagawa, Twir, V1adis1av, Viapx, Werdna, Xanzzibar, Выползень, 145 anonymous edits

Super Large Hadron Collider  Source: http://en.wikipedia.org/w/index.php?oldid=357640905 Contributors: Astavats, BenRG, Bngrybt, Bobo192, Calwiki, Courcelles, DaL33T, Dbiel,Discospinster, Epbr123, Father McKenzie, Fieldday-sunday, Franamax, Fumitol, HEL, HappyArtichoke, Headbomb, Jasonbuzz, Kay Dekker, Khukri, Kocio, Laurascudder, Materialscientist,MaverickFurmeson, OlEnglish, QuantumShadow, Rjwilmsi, Rtomas, Seba5618, Shadowjams, Skizzik, Ste1n, TechnoFaye, The Anome, WriterHound, Ygrange, Zorx12, 85 anonymous edits

Very Large Hadron Collider  Source: http://en.wikipedia.org/w/index.php?oldid=387263506 Contributors: Aly89, Andrewa, Anna Lincoln, Astavats, Azcolvin429, Bevo, CoRdigALZ,Dbachmann, Fatal!ty, Guy Thoreau, Halfdan, Headbomb, Iridescent, J.delanoy, JackSeoul, Joe446465446, Laurascudder, LeoNomis, Mac Davis, Northgrove, PMDrive1061, Ponty Pirate,RogueNinja, SCZenz, Salamurai, Science Guy, Seba5618, Skizzik, Tcncv, Verbal, ViperSnake151, WilliamH, Worm That Turned, XSG, Yin Huang, Zzuuzz, 44 anonymous edits

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Image Sources, Licenses and ContributorsImage:CERN logo.svg  Source: http://en.wikipedia.org/w/index.php?title=File:CERN_logo.svg  License: unknown Contributors: Ssolbergj

Image:CERN member states.svg  Source: http://en.wikipedia.org/w/index.php?title=File:CERN_member_states.svg License: Creative Commons Attribution 3.0 Contributors: User:Ssolbergj

File:Flag of Switzerland.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Flag_of_Switzerland.svg License: Public Domain Contributors: User:-xfi-, User:Marc Mongenet,User:Zscout370

File:Flag of Germany.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Flag_of_Germany.svg  License: Public Domain Contributors: User:Pumbaa80

Image:Cernfounders.png  Source: http://en.wikipedia.org/w/index.php?title=File:Cernfounders.png  License: GNU Free Documentation License Contributors: User:Hoshie, User:NerdyNSK

Image:CERN1999.png  Source: http://en.wikipedia.org/w/index.php?title=File:CERN1999.png  License: GNU Free Documentation License Contributors: User:NerdyNSK

Image:First Web Server.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:First_Web_Server.jpg  License: unknown Contributors: User:Coolcaesar at en.wikipedia

Image:Ciscosystemsrouteratcern.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:Ciscosystemsrouteratcern.jpg  License: GNU Free Documentation License Contributors:Coolcaesar

Image:Location Large Hadron Collider.PNG  Source: http://en.wikipedia.org/w/index.php?title=File:Location_Large_Hadron_Collider.PNG License: Creative CommonsAttribution-Sharealike 2.0 Contributors: User:Zykure

Image:Construction of LHC at CERN.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:Construction_of_LHC_at_CERN.jpg  License: GNU Free Documentation License Contributors: Andrius.v, Deadstar, Square87

Image:CERN-aerial.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:CERN-aerial.jpg  License: Creative Commons Attribution-Sharealike 2.5 Contributors: Moumou82, Schutz,Túrelio, 3 anonymous edits

Image:Bldng40cropped.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:Bldng40cropped.jpg  License: Creative Commons Attribution-Sharealike 3.0 Contributors: Gillis Danielsen

File:Flag of France.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Flag_of_France.svg  License: Public Domain Contributors: User:SKopp, User:SKopp, User:SKopp, User:SKopp,User:SKopp, User:SKopp

File:Flag of the United Kingdom.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Flag_of_the_United_Kingdom.svg  License: Public Domain Contributors: User:Zscout370

File:Flag of Italy.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Flag_of_Italy.svg  License: Public Domain Contributors: see below

File:Flag of Spain.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Flag_of_Spain.svg  License: Public Domain Contributors: Pedro A. Gracia Fajardo, escudo de Manual de ImagenInstitucional de la Administración General del Estado

File:Flag of the Netherlands.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Flag_of_the_Netherlands.svg License: Public Domain Contributors: User:Zscout370

File:Flag of Poland.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Flag_of_Poland.svg  License: Public Domain Contributors: User:Mareklug, User:Wanted

File:Flag of Belgium (civil).svg  Source: http://en.wikipedia.org/w/index.php?title=File:Flag_of_Belgium_(civil).svg License: Public Domain Contributors: Bean49, David Descamps,Dbenbenn, Denelson83, Fry1989, Howcome, Ms2ger, Nightstallion, Oreo Priest, Rocket000, Sir Iain, ThomasPusch, Warddr, Zscout370, 3 anonymous edits

File:Flag of Sweden.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Flag_of_Sweden.svg  License: Public Domain Contributors: Hejsa, Herbythyme, J budissin, Jon Harald Søby,Klemen Kocjancic, Lefna, Mattes, Meno25, Mormegil, Odder, Peeperman, Pl2241, Quilbert, Reisio, Sir Iain, Str4nd, Tabasco, Tene, Thomas Blomberg, Thuresson, Wiklas, Wouterhagens,Zscout370, 33 anonymous edits

File:Flag of Norway.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Flag_of_Norway.svg  License: Public Domain Contributors: User:Dbenbenn

File:Flag of Austria.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Flag_of_Austria.svg  License: Public Domain Contributors: User:SKopp

File:Flag of Greece.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Flag_of_Greece.svg  License: Public Domain Contributors: (of code) (talk)

File:Flag of Denmark.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Flag_of_Denmark.svg  License: Public Domain Contributors: User:Madden

File:Flag of Finland.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Flag_of_Finland.svg  License: Public Domain Contributors: User:SKopp

File:Flag of the Czech Republic.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Flag_of_the_Czech_Republic.svg License: Public Domain Contributors: special commission (of code): SVG version by cs:-xfi-. Colors according to Appendix No. 3 of czech legal Act 3/1993. cs:Zirland.

File:Flag of Portugal.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Flag_of_Portugal.svg  License: Public Domain Contributors: AFBorchert, ALE!, Afonso Silva, Anime AddictAA, Bluedenim, Boicote, Conscious, Denniss, DieBuche, Eddo, Er Komandante, Flad, FoeNyx, Fry1989, Herbythyme, Jelte, Kam Solusar, Klemen Kocjancic, Kookaburra, Mattes, Nick,Nightstallion, Reisio, Rkt2312, Skatefreak, Stunteltje, Thomas Gun, Thomas81, Tuvalkin, Zscout370, 30 anonymous edits

File:Flag of Hungary.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Flag_of_Hungary.svg  License: Public Domain Contributors: User:SKopp

File:Flag of Slovakia.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Flag_of_Slovakia.svg  License: Public Domain Contributors: User:SKopp

File:Flag of Bulgaria.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Flag_of_Bulgaria.svg  License: Public Domain Contributors: Avala, Denelson83, Fry1989, Homo lupus,Ikonact, Kallerna, Klemen Kocjancic, Martyr, Mattes, Neq00, Pumbaa80, SKopp, Scroch, Serjio-pt, Spacebirdy, Srtxg, Ultratomio, Vonvon, Zscout370, 9 anonymous edits

Image:CERN members.svg  Source: http://en.wikipedia.org/w/index.php?title=File:CERN_members.svg  License: GNU Free Documentation License Contributors: User:CrazyPhunk

Image:CERN-Membership-History.gif   Source: http://en.wikipedia.org/w/index.php?title=File:CERN-Membership-History.gif  License: GNU Free Documentation License Contributors:User:Bolonium, User:Hoshie, User:NerdyNSK

Image:CERN-Observers.png  Source: http://en.wikipedia.org/w/index.php?title=File:CERN-Observers.png  License: GNU Free Documentation License Contributors: User:NerdyNSK

File:Flag of SFR Yugoslavia.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Flag_of_SFR_Yugoslavia.svg License: unknown Contributors: Zscout370 at en.wikipedia

File:Flag of Romania.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Flag_of_Romania.svg  License: Public Domain Contributors: AdiJapan

File:Flag of Turkey.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Flag_of_Turkey.svg  License: Public Domain Contributors: User:Dbenbenn

File:Flag of Israel.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Flag_of_Israel.svg  License: Public Domain Contributors: AnonMoos, Bastique, Bobika, Brown spite, CaptainZizi, Cerveaugenie, Drork, Etams, Fred J, Fry1989, Himasaram, Homo lupus, Humus sapiens, Klemen Kocjancic, Kookaburra, Luispihormiguero, Madden, Neq00, NielsF, Nightstallion, Oren

neu dag, Patstuart, PeeJay2K3, Pumbaa80, Ramiy, Reisio, SKopp, Technion, Typhix, Valentinian, Yellow up, Zscout370, 31 anonymous editsFile:Flag of Russia.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Flag_of_Russia.svg  License: Public Domain Contributors: AVRS, AndriusG, Artem Karimov, Davepape, DmitryStrotsev, Drieskamp, Enbéká, Fred J, Gleb Borisov, Herbythyme, Homo lupus, Kiensvay, Klemen Kocjancic, Kwj2772, Mattes, Maximaximax, Miyokan, Nightstallion, Ondřej Žváček, Pianist,Pumbaa80, Putnik, R-41, Radziun, Rainman, Reisio, Rfc1394, Rkt2312, Rocket000, Sasa Stefanovic, SeNeKa, Srtxg, Stianbh, Wikiborg, Winterheart, Zscout370, Zyido, ОйЛ, 34 anonymousedits

File:Flag of Japan.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Flag_of_Japan.svg  License: Public Domain Contributors: Various

File:Flag of the United States.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Flag_of_the_United_States.svg License: Public Domain Contributors: User:Dbenbenn,User:Indolences, User:Jacobolus, User:Technion, User:Zscout370

File:Flag of India.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Flag_of_India.svg  License: Public Domain Contributors: User:SKopp

File:Flag of the United Nations.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Flag_of_the_United_Nations.svg  License: Public Domain Contributors: User:Denelson83,User:Madden, User:Zscout370, User:Denelson83, User:Madden, User:Zscout370

File:Flag of Europe.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Flag_of_Europe.svg  License: Public Domain Contributors: User:-xfi-, User:Dbenbenn, User:Funakoshi,User:Jeltz, User:Nightstallion, User:Paddu, User:Verdy p, User:Zscout370

File:Flag of Algeria.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Flag_of_Algeria.svg  License: Public Domain Contributors: User:SKopp

File:Flag of Argentina.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Flag_of_Argentina.svg  License: Public Domain Contributors: User:Dbenbenn

File:Flag of Armenia.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Flag_of_Armenia.svg  License: Public Domain Contributors: User:SKopp

File:Flag of Australia.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Flag_of_Australia.svg  License: Public Domain Contributors: Ian Fieggen

File:Flag of Azerbaijan.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Flag_of_Azerbaijan.svg License: Public Domain Contributors: Alex Spade, Brandmeister, Charismaniac,Dbenbenn, Denelson83, Enbéká, Er Komandante, Fry1989, Homo lupus, Jacobolus, Mattes, NTK, Neq00, Proger, Reality006, SKopp, Sir Iain, ThomasPusch, Tiptoety, Zscout370,   05, 9نام جرتanonymous edits

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File:Flag of Belarus.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Flag_of_Belarus.svg  License: Public Domain Contributors: Andrew c, Bender235, Denelson83, Gmaxwell,Homo lupus, Joey-das-WBF, Klemen Kocjancic, Liftarn, Neq00, Nightstallion, Permjak, Pianist, Pumbaa80, Sir Iain, SndrAndrss, Str4nd, Takadraka, Vzb83, Zscout370, ОйЛ, 12 anonymousedits

File:Flag of Brazil.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Flag_of_Brazil.svg  License: Public Domain Contributors: Brazilian Government

File:Flag of Canada.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Flag_of_Canada.svg  License: Public Domain Contributors: User:E Pluribus Anthony, User:Mzajac

File:Flag of Chile.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Flag_of_Chile.svg  License: Public Domain Contributors: User:SKopp

File:Flag of the People's Republic of China.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Flag_of_the_People's_Republic_of_China.svg License: Public Domain Contributors:User:Denelson83, User:SKopp, User:Shizhao, User:Zscout370

File:Flag of Colombia.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Flag_of_Colombia.svg  License: Public Domain Contributors: User:SKopp

File:Flag of Croatia.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Flag_of_Croatia.svg  License: Public Domain Contributors: AnyFile, Argo Navis, Denelson83, Denniss, Dijxtra,Klemen Kocjancic, Kseferovic, Minestrone, Multichill, Neoneo13, Nightstallion, O, PatríciaR, Platonides, R-41, Rainman, Reisio, Rocket000, Suradnik13, Zicera, Zscout370, 5 anonymous edits

File:Flag of Cuba.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Flag_of_Cuba.svg  License: Public Domain Contributors: see below

File:Flag of Cyprus.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Flag_of_Cyprus.svg  License: Public Domain Contributors: AnonMoos, Consta, Dbenbenn, Denelson83,Duduziq, Er Komandante, Homo lupus, Klemen Kocjancic, Krinkle, Mattes, NeoCy, Neq00, Nightstallion, Oleh Kernytskyi, Pumbaa80, Reisio, Telim tor, ThomasPusch, Vzb83, 15 anonymousedits

File:Flag of Estonia.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Flag_of_Estonia.svg  License: Public Domain Contributors: User:PeepP, User:SKopp

File:Flag of Georgia.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Flag_of_Georgia.svg  License: Public Domain Contributors: User:SKopp

File:Flag of Iceland.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Flag_of_Iceland.svg  License: Public Domain Contributors: User:Ævar Arnfjörð Bjarmason

File:Flag of Iran.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Flag_of_Iran.svg  License: unknown Contributors: Various

File:Flag of Ireland.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Flag_of_Ireland.svg  License: Public Domain Contributors: User:SKopp

File:Flag of Lithuania.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Flag_of_Lithuania.svg  License: Public Domain Contributors: User:SKopp

File:Flag of Macedonia.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Flag_of_Macedonia.svg License: Public Domain Contributors: User:Gabbe, User:SKopp

File:Flag of Mexico.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Flag_of_Mexico.svg  License: Public Domain Contributors: User:AlexCovarrubias, User:Zscout370

File:Flag of Montenegro.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Flag_of_Montenegro.svg  License: Creative Commons Attribution-Sharealike 3.0 Contributors:User:B1mbo, User:Froztbyte

File:Flag of Morocco.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Flag_of_Morocco.svg  License: Public Domain Contributors: User:Denelson83, User:Zscout370

File:Flag of New Zealand.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Flag_of_New_Zealand.svg License: Public Domain Contributors: Adambro, Arria Belli, Bawolff,Bjankuloski06en, ButterStick, Denelson83, Donk, Duduziq, EugeneZelenko, Fred J, Fry1989, Hugh Jass, Ibagli, Jusjih, Klemen Kocjancic, Mamndassan, Mattes, Nightstallion, O, Peeperman,Poromiami, Reisio, Rfc1394, Shizhao, Tabasco, Transparent Blue, Väsk, Xufanc, Zscout370, 35 anonymous edits

File:Flag of Pakistan.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Flag_of_Pakistan.svg  License: Public Domain Contributors: Abaezriv, AnonMoos, Badseed, Dbenbenn,Duduziq, Fry1989, Gabbe, Himasaram, Homo lupus, Juiced lemon, Klemen Kocjancic, Mattes, Mollajutt, Neq00, Pumbaa80, Rfc1394, Srtxg, ThomasPusch, Túrelio, Zscout370, 8 anonymousedits

File:Flag of Peru.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Flag_of_Peru.svg  License: Public Domain Contributors: User:Dbenbenn

File:Flag of Serbia.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Flag_of_Serbia.svg  License: Public Domain Contributors: ABF, Avala, B1mbo, Denelson83, EDUCA33E,Herbythyme, Imbris, Nightstallion, Nikola Smolenski, Nuno Gabriel Cabral, R-41, Rainman, Rokerismoravee, Sasa Stefanovic, Siebrand, ThomasPusch, Túrelio, Zscout370, 7 anonymous edits

File:Flag of Slovenia.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Flag_of_Slovenia.svg  License: Public Domain Contributors: User:SKopp, User:Vzb83, User:Zscout370

File:Flag of South Africa.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Flag_of_South_Africa.svg  License: Public Domain Contributors: User:SKopp

File:Flag of South Korea.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Flag_of_South_Korea.svg  License: Public Domain Contributors: Various

File:Flag of the Republic of China.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Flag_of_the_Republic_of_China.svg License: Public Domain Contributors: 555, Bestalex,Bigmorr, Denelson83, Ed veg, Gzdavidwong, Herbythyme, Isletakee, Kakoui, Kallerna, Kibinsky, Mattes, Mizunoryu, Neq00, Nickpo, Nightstallion, Odder, Pymouss, R.O.C, Reisio, Reuvenk,Rkt2312, Rocket000, Runningfridgesrule, Samwingkit, Shizhao, Sk, Tabasco, Vzb83, Wrightbus, Zscout370, 72 anonymous edits

File:Flag of Thailand.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Flag_of_Thailand.svg  License: Public Domain Contributors: Andy Dingley, Chaddy, Duduziq, Emerentia,Gabbe, Gurch, Homo lupus, Juiced lemon, Klemen Kocjancic, Mattes, Neq00, Paul 012, Rugby471, Sahapon-krit hellokitty, TOR, Teetaweepo, Xiengyod, Zscout370, Δ, 22 anonymous edits

File:Flag of Ukraine.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Flag_of_Ukraine.svg  License: Public Domain Contributors: User:Jon Harald Søby, User:Zscout370

File:Flag of Vietnam.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Flag_of_Vietnam.svg  License: Public Domain Contributors: user:Lưu Ly

Image:CERN Globe of Science and Innovation.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:CERN_Globe_of_Science_and_Innovation.jpg License: Creative CommonsAttribution-Sharealike 2.0 Contributors: Lysippos, TomAlt

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Image:ALICE Detector.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:ALICE_Detector.jpg  License: Public Domain Contributors: Connor Behan

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Image:ATLAS TRT.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:ATLAS_TRT.jpg  License: GNU Free Documentation License Contributors: Gorgo, Harp

Image:ATLAS HCal.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:ATLAS_HCal.jpg  License: GNU Free Documentation License Contributors: Mdd, Pieter Kuiper, Skaller, 1anonymous edits

Image:CERN-Rama-33.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:CERN-Rama-33.jpg  License: Creative Commons Attribution-Sharealike 2.0 Contributors: User:Rama

Image:ATLAS Above.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:ATLAS_Above.jpg  License: GNU Free Documentation License Contributors: Gorgo, Harp

Image:Atlas detector CERN feb2007.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:Atlas_detector_CERN_feb2007.jpg  License: Public Domain Contributors: Sindre Skrede

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Image:Lead Tungstate Crystal Preparation.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:Lead_Tungstate_Crystal_Preparation.jpg License: unknown Contributors: Jz 007,Luxo

Image:CMS Hcal 26 01 2007.JPG  Source: http://en.wikipedia.org/w/index.php?title=File:CMS_Hcal_26_01_2007.JPG License: GNU Free Documentation License Contributors: Luxo,Murielvd

Image:HCAL Prepared for insertion.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:HCAL_Prepared_for_insertion.jpg License: unknown Contributors: David Barney

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Image:Tracker FED Testing.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:Tracker_FED_Testing.jpg  License: unknown Contributors: S. Boreham

Image:Insertion of vac-tank 2.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:Insertion_of_vac-tank_2.jpg  License: unknown Contributors: Harp, Luxo, WikipediaMaster

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Image:Run62063ev2433.png  Source: http://en.wikipedia.org/w/index.php?title=File:Run62063ev2433.png  License: unknown Contributors: CMS Collaboration

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Image:First Gold Beam-Beam Collision Events at RHIC at 100 100 GeV c per beam recorded by STAR.jpg  Source:http://en.wikipedia.org/w/index.php?title=File:First_Gold_Beam-Beam_Collision_Events_at_RHIC_at_100_100_GeV_c_per_beam_recorded_by_STAR.jpg  License: Creative CommonsAttribution-Sharealike 2.0 Contributors: Dbc334, Dmgultekin, Doodledoo, FlickreviewR, Herald Alberich, Kuaile Long, Odie5533, Romanm, Roomba, Saperaud, Yarnalgo, 4 anonymous edits

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