First Results of ATLAS at the LHC -- The rediscovery of the Standard Model--

Marcel Vreeswijk (Nikhef/UvA-IoP)

First Results of ATLAS at the LHC

--The rediscovery of the Standard Model--

Contents:• Intro: The Standard Model

Elementairy particles.

• Status LHC and ATLAS

• Physics results 2010

The Standard Model

So, what have we been doing in 2010?

Measuring ‘backgrounds’!

Higgs mechanisme to generate mass!Higgs boson mass > 114 GeV

Ultimate goal:

detect the Higgs particle

(not yet;need more data!)


CERN site

LHCP+P at 7TeV27km60 ton He at 2K 4 big experiments this talk: ATLAS

First year of running. (7TeV)high quality data 2010: ~35pb-1

In 2011: run at 7TeV or higher? >>10-fold luminosity?

The LUMINOSITY represents the delivered number of proton collisions

In addition: Pb+Pb collisions (not in this talk)

atlas

Large Hadron Collider (LHC)


LHC physics reach

• Production Cross-section of top quarks and W, Z bosons are measurable with 2010 data!

• Top, W,Z signals are important:1.Standard candles for calibration2.Background to new physics & Higgs

searches

1000

1

1 M

5 T

# events in 2010

HiggsTop quarksW,Z bosons

Proton-Proton

In r

each

in 2

010

Higgs W, Z

W, ZPromising final states:H W+W- 2 leptons + EtMissH ZZ 4 leptonsAlso H 2 photons

7TeV in 2010

jargon: lepton=electron or muon

N = L . N = # collisionsL = Luminosity = cross-section


Inner detector(charged particle tracks)

Calorimeter(energy all particles, but muons) Muon ‘Chambers’

ATLAS

p

Data rec. 93.5%#working channels >99%


Performance Inner Tracker

1 m

Inner Tracker

Ks

Kaon discovery: 1947

Pixel detector (80M channels)Silicon strips (6M channels)TRT (350k channels)Operational for 97.5%

Momentum measurement in magnetic field of 2TResolution σ(pT)/pT = 0.05%pT 1% ⊕


Performance Calorimeterelectromagnetic: Liquid Argon sampling calorimeter.Resolution ~10%/sqrt(E)Granularity: eta x phi=0.025 x 0.025

since 1950

Rediscovery of the 0 8m


Di-jet physics


Di-jet invariant mass

• New energy domain.

• Highest Pt jet: 1.12 TeV

• Highest mass: 3.7 TeV

• Searches for new physics ongoing

ATLAS published 3 papers on jet measurements

p p

jet

jet


Performance Muons

Physics signals show up!

Muon system:1200 Muon chamber350k drift tubes(air core toroidal field 0.5T)

Designed for TeV muons (not yet)

Z boson ‘rediscovered’Originally: 1983 at CERNMass: 91.19 GeV


Muon resonancesATLAS 2010

? mass

Pub

lishe

d20

10

Z cross-section in new energy domain=7TeV

1960

1963

1977

1974

1983


MissingTransverse energy

W boson ‘rediscovered’Originally: 1983 at CERNMass: 80.4 GeV


W boson production

W decays to muon + (unseen) neutrino. Missing transverse energy.

W

q

q’g

Transverse W mass:


Top pair (ttbar) production• complicated events:1. Many jets with 2 b-jets (can

be ‘tagged’)2. Electron or Muon3. EtMiss Standard candle New physics may show up p pt

t ttbar has two measurable decays modes:single-leptondi-lepton(mode is set by W decay)

ttbarsingle-lepton

DatumBasic prper.Europ. Topds!Last heaviest known particleLast before new


di-leptonic ttbar2 b-tagged jets


ttbarMore info on poster by Ido & Hegoi N. from Nikhef

Van Tera naar 100evts selectieSpeld hooi


ttbar: theory & experiment


Higgs in 2011 ?

We have measured the ‘backgrounds’, now we are ready for the signal !

Conclusion

The LHC and the ATLAS detector have demonstrated to be ready for the Standard Model Higgs or new physics

See next talk by Paul de Jong!


BACKUP

4222V

“We know everything about the

Higgs boson except its mass”

Λ (GeV)

Hig

gs m

ass (

GeV

)

Triviality

Vacuum stability

Limits on mh from theory

Limits on mh from exper.


W boson cross section


Photon production (QCD compton)• photons of hundreds of GeVs !

• (Xray 0.0001 GeV)




The Standard Model

Ultimate goal: detect the Higgs particle (not yet…need more data!)

So, what have we been doing in 2010? Measuring ‘backgrounds’!

+ Higgs boson to generate mass!

Promising decay modesH 2 photonsH W+W- 2 leptons + EtMissH ZZ 4 leptonsand much more….


The Standard Model

• Production Cross-section of top quarks and W, Z bosons are measurable with 2010 data!

• Top, W,Z signals are important:1. Standard candles for calibration2. Background to new physics & Higgs

searches

1000

1

1 M

5 T

# events in 2010

HiggsTop quarksW,Z bosons

Proton-Proton

In r

each

in 2

010

Note: a proton=many quarks+gluons

Higgs W, Z

W, ZPromising final states:H W+W- 2 leptons + EtMissH ZZ 4 leptonsAlso H 2 photons

7TeV in 2010

jargon: lepton=electron or muon


CERN site

LHCP+P at 7TeV27km60 ton He at 2K 4 big experiments this talk: ATLAS

First year of running. (7TeV)high quality data 2010: ~35pb-1This year (2011): run at 7TeV or higher? >>10-fold luminosity?

The LUMINOSITY represents the delivered number of proton collisions

3.2T botsingen655k hi Pb=Pb


Z boson production Do we understand Z production and its backgrounds? First measurement ever at 7 TeV.

Ook in e+e-DiagrammenLin schaal?

DatumZ massa2Gev wordt 90GeV

Documents

First Results of ATLAS at the LHC -- The rediscovery of the Standard Model--