Particle Physics II

Chris Parkes

Beyond the Standard Model:

Neutrinos, SUSY, dark matter

• Solar neutrino problem

• Neutrino oscillations

• Supersymmetry

•Astro-particle physics: Dark matter, high-energy cosmic rays

5th Handout

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Neutrinos in SM• Massless• Left-handed• Only weak interactions (no EM, strong)• Electron,muon,tau neutrinos

• Only 3 (with mass <Mz/2)

Revision

Beyond the SM• Neutrino Oscillations

– Neutrinos have mass

• Only BSM phenomena discovered– As yet experiments have not resolved how to include in theory

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• Electron neutrino• Suggested to ensure

energy conservation in

Nuclear beta decay

eepn Pauli, 1931

"Dear radioactive ladies and gentlemen",

enpe

(also detected neutron)

Observed two photons from positron-electron annihilation

Scintillator

Water

Scintillator

e

p e++e-

PM

PM

γ

γ

ee

Neutrino Discovery

•Discovered through inverse beta decay on water target using anti-neutrinos from a nuclear reactor

F. Reines 1956

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Muon Neutrino• Identification that there are different types of neutrino• Proton beam on Be target produces Pions• Pions decayExperiment

– Large iron filter – absorb everything except neutrinos– (heavy) target & tracking detector to interact with neutrinosProduce muons ?

Or electrons?

Only muons seen, hence

Tau Neutrino•Tau discovered as resonance in e+e- in 1975•Assumed to have neutrino, and missing momentum observed in decays•3 neutrinos measurement at LEP from z lineshape•Direct observation in 2000 (latest SM particle to be discovered)

pn np

Lederman, Schwartz, Steinberger1962

pen nep

e

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Solar neutrino problem

• Sun produces neutrinos in several nuclear interactions– e.g. pp fusion

– Well known from solar models

– Expect N(e)=6.4x1010e cm-2s-1 at earth

• (64 billion through your fingernail per second)

– Measure rate….

eeHpp 2

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Solar neutrino’s & Cleaning Fluid390m3 (520tons) of cleaning fluid C2Cl2~1030 37Cl atoms

e+37Cl37Ar+e

Flush~1/month with He and separate 37ArLook for 37Ar decay via 2.8KeV K-shell x-raySolar model predicts 7.6±1.3 SNUMeasure 2.56±0.6±0.15 SNU

Deep (1600m) underground to shield from cosmic rays

SNU = Solar Neutrino Unit1 SNU= one capture per 1036 atoms s-1

Homestake Mine, South Dakota

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Solar neutrino problem

Discrepancy between e predicted by solar model and measured– Homestake mine

(Cl)– Kamiokande

(water)– Gallium expts

Homestake mine

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Sudbury Neutrino Observatory (SNO)• SNO: 1000 tonnes D20, 10000 PMTs

Sensitive to:Charged current interaction: e+dp+p+e- 0.35±0.02 SSM

Neutral current: x+d n+p+x 1.01±0.12 SSM

e only

e,,

(also elastic scattering, not discussed here)

SSM=solar standard Model

•Current number of neutrinos

•Deficit of electron neutrinos

•Electron neutrinos have oscillated to other types

2002

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Detection – Cherekov light• Charged current:

– Highly energetic electron• 2000 times lighter than proton

– Travels faster than local speed of light

• Cherenkov light given off• Analagous to sonic boom

– Detect light in PMTs

• Neutral current:– Neutron captures on deuteriumnucleus – giving off 6 MeV photon

• photon interacts with electrons giving off Cherenkov light

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Neutrino mixing

• Similar to the case we discussed for Kaons

3

2

1

321

321

321

UUU

UUU

UUU eeee

Flavour states and mass states analogous to the quarks

PMNS matrix

Three mixing angles,θ23~45o

Electron ν

Muon ν

Tau ν

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Implications• Neutrinos oscillate

have mass• Oscillations depend on square of mass differences

– (m1-m2)2=8x10-5 eV2, (m2-m3)2=2x10-3 eV2

• Unlike K (or B) meson oscillations there are three eigenstates

lepton flavour violation First results beyond standard model of particle physics!

How neutrinos can be included in theory not yet understoodExperiments underway….One of mixing angles unknown, CP violation ?, mass order…

T2K neutrino beam to Super Kamiokande,neutrinoless double beta decay experiments

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Supersymmetry• In Q.M. connection between• Global transformations and conserved quantities, e.g.• Translational Invariance Linear momentum conservation• Rotational InvarianceAngular momentum conservation• Translations in timeEnergy conservation

Noether’s theorem – Symmetries (invariances) naturally lead to conserved quantities

Finding symmetries now a guiding principle in new physical theories

Propose new symmetry of nature: SupersymmetrySpin ½ Fermions (quarks, leptons) spin 0 boson superpartnerSpin 1 Bosons spin ½ fermion superpartner

SUSY not an exact symmetryMass of SUSY particles ≠Mass of normal particles

Since none discovered yet

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SUSY particles

Interactions are the same e.g. squarks interact via strong interaction

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SUSY Motivation

4. SUSY provides a theoretical route to include gravity in “standard model”, and needed in string / M-theory

1/S

tren

gth

Log Energy GeV

1. SUSY allows unification of the forces 2. SUSY cancels divergences in SM

SUSY: theoretically beautiful and convenient – but is it true ?

3. Lightest SUSY particle (LSP) is candidate for dark matterMost models LSP is stable neutralino

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SUSY Experimentally• “normal” particles and “SUSY” particle have opposite R-parity• R-Parity conserved (assumed!)• R-parity conservation stable LSP Neutralino, neutral weakly interacting particle

missing energy in event, key signature!

• Measure missing transverse momentum/energy

Candidate event in D0(TeVatron)

No evidence

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Dark Matter• Compelling astrophysical evidence

for dark matter– e.g. rotation curves

of spiral galaxies

• ‘dark matter’ is a term of ignorance– Neutrinos, small contribution– Weakly Interacting Massive Particles (WIMPs) ?

• e.g. SUSY neutralino

Expected no DM

Observed

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Dark Matter Searches

1. Collider expts (as discussed)

2. Direct Detection Experiments

3. WIMP annihilation

e.g. CDMS, detect the heat produced when a particle hits an atom in a crystal of germanium, operates at 10mK

e.g. Gamma- ray space telescope - FERMI, detect gamma rays from WIMP annihilation.Launched June 2008

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High Energy Cosmic rays• Pierre Auger Observatory •Detect ultra-high-energy cosmic

rays: single particles E > 1020 eV •(c.f. tennis serve).

•Rate 1 per km2 per century•Source: Proton accelerated by magnetic fields of black-holes in active galactic nuclei ?

•Cosmic ray reacts in atmosphere•shower 109 particles

•1600 water cherenkov detectors•3000 Km2 in Argentina(also flourescence detectors)

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Physics beyond the standard model• SM almost complete

– But still a Higgs to find…..• Neutrinos: first physics BSM

– Neutrino oscillations neutrino mass• Some big unanswered questions in SM

– Why is there more matter than anti-matter in the universe ?– What is Dark Matter / Dark Energy– Why three generations ? Why hierarchy of mass scales ?– How to incorporate gravity ?

• Supersymmetry– Allows unification of the forces– Allow inclusion of gravity– BUT not observed yet,

• Many other possibilities– Extra dimensions, Compositeness

• But so far no evidence!• Wide experimental programme

– LHC is biggest highest profile project– Many other active experiments

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Start of the LHC

xkcd.com

You tube: LHC rap

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Start of the LHC - September 2008• First beams

circulated round full ring

• Particles seen in all detectors

The First Event22nd August 2008

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Friday 19th September 2008• CERN Press Release: Incident in LHC sector 34• Geneva, 20 September 2008. During commissioning (without beam) of the

final LHC sector (sector 34) at high current for operation at 5 TeV, an incident occurred at mid-day on Friday 19 September resulting in a large helium leak into the tunnel. Preliminary investigations indicate that the most likely cause of the problem was a faulty electrical connection between two magnets, which probably melted at high current leading to mechanical failure.

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November / December 2009

• First Collisions

• World Record collision Energy, 2.36 TeV

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Calibration & Detector Performance• Re-finding particles• Measuring Resolutions

σ = 4.3 ± 0.1 MeV/c2

M(Ks) = 497.3 ± 0.2 MeV/c2

M(KsPDG) = 497.7 MeV/c2

3µm

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First Results

•Already two publications – number of charged particles•Prelim. results on particle rates and ratios

KShort pt distribution integratedKShort pt distribution integrated

Black: Data 2009Red: MCBlue : background

prel.

Charged Particles

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2010 Status• Shutdown for repairs & servicing

• Operations started again at end of February

• Hope to increase collision energy to

~ 7 TeV this month

• Significant Physics results expected from 2010-2011 run

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Large Hadron Collider

• 2008: “It’s the end of the world as we know it”End of the world postponed as broken Hadron Collider out of commission for months

•2010 onwards: “It’s the end of physics as we know it” ?•Higgs, Susy, Dark Matter, matter anti-matter asymmetry…..

Not the time for speculation, but to wait (a little longer) and see what Nature has in store….