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Физика на больших детекторах LHC

How to observe new physics at LHC

Alexandre Rozanov16.01.2011

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Outlook

• Standard Model at 7 TeV• Higgs • SUSY• New physics from dijets (q*,Black Holes, contact interactions)• new W

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LHC status Instant luminosity record 2010 2 10 32 cm-2 s-1

Integrated luminosity today 45 pb-1

Hope to collect at end of 2011 1000 pb-1

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tt cross section • ATLAS and CMS measured on small sample tt cross-section compatible with SM

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Quark-gluon plasma in Pb-Pb collisions • jet quenching in Pb-Pb collisions• J/ψ yield• Z yield

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Quark-gluon plasma in Pb-Pb collisions • jet quenching : centrality dependent di-jet asymmetry• centrality dependent suppression in the normalised J/ψ yield• no visible effect for Z

Spectacular events observed

The first ZZ4µ event

Spectacular events observedHighest mass dijet: Mjj =3.7 TeV ET jet1 ~ 670 GeV

ET jet2 ~ 610 GeV

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Decisions after Chamonix meeting• Run in 2011• 2011 max peak luminosity 1.3-2.0 1033 s-1 cm-2 • Integrated luminosity: 1 fb-1 in 2011 (but

potentiality to get much more)• Energy 3.5 x 3.5 = 7 TeV in 2011 • Squeeze β*= 1.5 m • Bunch separation 75 ns or 50 ns • Number of bunches nb=936-1404

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Decisions after Chamonix meeting• Continue run in 2012 • Integrated luminosity: 5 fb-1 in 2012 (but

potentiality to get much more)• Reconsider 8 TeV for 2012 (depends on the

results of the splice measurements with “Thermal Amplifier”)

• Longer 2011/2012 Xmas stop for electrical/ventilation maintenance

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LHC versus TevatronTevatron ~5-10 fb-1 with √s=1.96 TeV

LHC ~1 fb-1 with √s=7 TeV at end of 2011

LHC advantage – gain in energy 2->7 TeV

LHC temporary disadvantage – loss in luminosity

H->WW at mH=160 GeV LHC gain factor 15 (gg)

Z’ at mZ’=1 TeV LHC gain factor 100 (qq)

Higgs

• Higgs production at LHC

SM Higgs branching ratios

Higgs branching ratios

bb ττ

ZZWW

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Motivation for low mass HiggsMotivation for low mass Higgs

222H GeV/c 90m 27

2H GeV/c114.4m 2

H TeV/c1m (LEP) et (WW scattering unitarity) (electroweak fits) mH < 149 GeV at 95% CL

mh < 90 GeV in MSSM without radiative corrections mh < 130 GeV in MSSM with radiative corrections Aleph LEP Higgs candidate mH=115 GeV

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How Higgs → should looks likeHow Higgs → should looks like

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First results in ATLAS

• L = 37 pb-1

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Projected sensitivity for H→

• L = 1 fb-1 in 2011• Possibility to exclude Higgs with mH=110-140 GeV at

3.2-4.3 σSM 95% CL

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W H→ bb

• also ZH, ttH• good b-tagging, better signal when H is boosted

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qq H→ ττ

• production via Vector boson fusion• good b-tagging, better signal when H is boosted

SM Higgs with mH > 130 GeV• Events observed with

4e, 4 and 2e2 final states• Clear mass peak with S/B >> 1• most sensitive around mH=200 GeV

SM Higgs, H->ZZ->4l

• Very clean signature– Narrow resonance– Small background contribution

• Main experimental issues– Lepton isolation

• Zbb and ttbb rejection• Good for discovery in wide Higgs mass range

– 130 < MH < 600 GeV ATLAS

Search for H W W* l l • H W W* dominates • need H W W* l l • no peak, shape close to background• mT=√((∑Eti)2 - (∑pi)2)• 0j – gluon fusion• 1j or 2 j – Vector Boson Fusion

0 jets

1 jets

2 jets

SM Higgs with mH = 130-300 GeV• H W W* dominates • need H W W* l l • no peak, shape close to background• mT=√((∑Eti)2 - (∑pi)2)• 0j – gluon fusion• 1j or 2 j – Vector Boson Fusion

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Higgs discovery potential 2011-2012

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Higgs exclusion potential

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• 95% CL exclusion is possible in 2011-2012 in the full mass range • 3 sigma Higgs observation looks possible in the full mass range in 2011-2012,

especially if optimization of analysis will be done at low mass and partial running at 8 TeV

• 5 sigma discovery at low and very high mass Higgs should wait for design energy and luminosity after 2015

Higgs discovery-exclusion potential

A.Rozanov ITEP Winter School of Physics February 2006 27

MSSM Higgs• Minimal super-symmetric extension of Higgs sector

– Five Higgs: h (light), H(CP-even), A(CP-odd), H (heavy)– Parameter space reduced to two: MA,tanβ (ratio of vev of two Higgs doublets)– Theoretical limit on light MSSM Higgs: h<135 GeV

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MSSM Higgs• Large multiplicity of discovery modes:

– SUSY particles heavy:• SM-like: h,bb,,WW; H4l• MSSM-specific: A/H,,tt; Hhh, AZh; H, c s

– SUSY accessible:• H/A 0

2 02, 0

2 h 01

• Small impact on Higgs branching ratio to SM particles• Consider different MSSM scenarios

– Different upper limits to light MSSM Higgs (h)

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• Associated production with b-quarks dominate bbH • Very clean signature of two muons and b-jets• Typical branching B=4 10-4 and σ =100 pb for mA/H=150 GeV tanβ=40 • Background Z+jets, tt (leptonical)

H/A →µµ

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• tanβ <1, mH < mt , production tt→bH+ bW

• triger by leptonic W decay

• signature of lepton, missing ET , two light jets and two b-jets

• mH reconstructed from two light jets

• Background : semi-leptonic tt

H/A →cs

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• tanβ > 1, mH < mt , production tt→bH+ bW

• triger by leptonic W decay and leptonic τ decay

• signature of two opposite charge leptons, missing ET and two b-jets

• exploit stronger peaking to -1 of lepton on H side• Background : leptonic tt

H/A →τν

Early LHC SUSY search

• see lecture of D.Kazakov СУСИ расширение Стандартной Модели • SUSY best candidate for early discovery• Gluino ans Squark strongly produced • QCD comparable cross-section – 100 events/day at L=1033 and m(gluino)~ 1 TeV• ETmiss from LSP escaping detection• High ET jets if unification of gaugino mass assumed• Spherical events: Tevatron - Mg,q > 400 GeV• Multiple leptons: decay of charginos/neutralinos

SUSY stabilizes mH SUSY at TeV scale spectacular signatures at LHC

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Inclusive SUSY signatures

• A typical SUSY event at LHC will contain hard jets + n leptons and large missing transverse energy, ET .

• The SUSY mass scale:

• The effective Mass gives a handle on the SUSY mass scale

• Cuts to reject SM background– 4 jets with PT > 50GeV

– 2 jets with PT > 100GeV

– ET > max(0.2Meff,100GeV)– no lepton

SUSYmissT

4iTeff MEpM

i

g~

Lq~q 0

2χ~

h,Z

01χ~

p

),min( q~g~SUSY mmM

ATLAS 20.6fb−1

SM background

SUSY signal (full sim.)

q

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MSUSY vs. Effective mass

• Plot MSUSY vs. the peak value of

the Meff (from full simulation).

• Repeat this for different mSUGRA

models. (Minimal Supergravity

Mediated SUSY breaking)

• Correlation line from fast

simulation

• Meff can be used over a broad

range of mSUGRA models.

Meff is a good variable for the estimation of the SUSY mass scale

ATLAS

SUSY

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Z

q

q

02

q~g~

Backgrounds for ETmiss• Real ETmiss from neutrino in W, Z+jets,tt• Instrumental ETmiss from mismeasured multi-jets (dead/hot cells, non-gaussian tails, gaps in acceptance etc)• Reject events with fake ETmiss : beam-gas, displaced vertexes, hot cells, ETmiss along jets, jets in gaps. • All detector and machine garbage end up in ETmiss trigger

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Performance of missing ET

• Based on calorimeters and muons• some cleaning from cosmics and beam backgrounds

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SUSY search without lepton • Direct gluino pairs (A)

• Associated gluino-squark (B)• Low mass squark anti-squark (C)• High mass squark anti-squark (D)

event’s maximal lower bound for the mass for either primary outgoing particle (e.g. squark in the signal) under the assumption that each decayed to one of the leading two jets in additionto a source of ~PTmiss (e.g. a neutralino, assumed to be massless)

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SUSY search without lepton

ATLAS preliminaryATLAS preliminary

ATLAS preliminaryATLAS preliminary

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mSUGRA limits without lepton

mgluino(mSUGRA) <775 GeV at 95% CL

SM background – 1 lepton

SM cuts+1lepton

g~

Lq~q 0

2χ~

l~

l

01χ~

p

q l

Signal reduced to 20-40% of no lepton mode

• S/B better than in 0-lepton mode. Clean

discovery mode

• QCD-multijets suppressed with fake

leptons

• tt- dominant, but more predictable

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SUSY search with one lepton • at least 3 jets pT > 60, 30, 30 GeV

• One lepton pT > 20 GeV• mT > 100 GeV• MET/meff > 0.25• meff > 100 GeV• backgrounds W+jets, tt, single top,QCD • Extrapolation from control regions to signal region

• 95% CL limits • Electron 0.065 pb (2.2 events)• Muon 0.073 pb (2.5 events)

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mSUGRA limits with one lepton

mgluino(mSUGRA) <700 GeV at 95% CL

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Perpectives SUSY in 2011

Cosmologicaly interesting

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Di-jet eventmj1j2

=1.77 TeVpT j1= 1.1 TeVpT j2= 0.48 teVpT j3= 0.16 TeVpT j4= 0.10TeV

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Di-jet resonances

• pT j1> 80 GeV pT j2> 30 GeV• |ηj1|<2.5 |ηj2|<2.5 |Δη|<1.3

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Exclusion of the exited quark

• qg-fusion production and dijets decays • Λ=mq* compositeness scale • f=f’= fs=1 coupling parameters• 95% CL limit• ATLAS exclude mq* < 2.15 TeV • CDF exclude mq* < 870 GeV

Black Holes At The LHC

σ ~ πRS2 ~ O(100)pb

LHC Black Hole Factory

BH lifetime ~ 10-27 – 10-25 seconds

Decays with equal probability to all particles via Hawking Radiation

If Mpl ~ O(1 TeV) Black Hole Production possible at LHC

MBH = √S

Rs

Parton

Parton

Rs = Schwarzschild radius2

2

c

GM BH

N.Arkani-Hamed, S. Dimopoulos and G.R.Dvali [hep-ph/9803315]S.Dimopoulos and G. Landsberg [hep-ph/0106295]

MBH~MPL: Study Quantum Gravity at the LHC

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Randall-Meade Quantum Black Hole model quantum gravity mass scale MD

Black Holes

BlackMax black hole event generatorMD > 3.67 TeV for n = 6 extra dimensions

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Gravitons be produced with a range of masses at LHC Randall-Sundrum (RS) gravitons no limit yet as expected rate is too low

Gravitons

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Contact interactions in di-jets• QDC background: rather forward jets, mainly in t-channel g exchange • New contact interactions: isotropic widely separated jets• pT j1 > 60 GeV pT j2 > 30 GeV • |ηj1|<2.8 |ηj2|<2.8• rapidity y = 0.5 ln((E+pz)/(E-pz)) , y*=0.5(y1-y2)• |y1+y2|<1.5•

• Fχ = N (|y*| < 0.6) / N (|y*| < 1.7)

η or Fχ

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Dijet contact interaction

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Dijet contact interaction• Data well described by standard model (QCD Pythia)

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Dijet contact interaction limit• qqqq contact interaction• • From Fχ ratio mq* > 2.6 TeV at 95% CL • Limit on the scale of contact interaction Λ > 7.9 TeV at 95% CL from Fχ• Preveous limit from Tevatron Λ > 2.0 TeV

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Search for W’ or W* in ATLAS • W’ same couplings as in Standard Model, W* - magnetic type couplings• W’ with mW’ =1 TeV at √s=7TeV expect σ*Acceptance (eνe): ~300fb• D0 result mW’ < 1 TeV at 95% CL • e candidate with ET> 20 GeV |η|<2.5• ETmiss >25 GeV • mW’ < 1.49 TeV at 95 % CL • mW* < 1.49 TeV at 95 % CL

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After 2012

• Long 19 months shutdown in 2013-2014: • replace all splices with new clamped and Cu shunted• add pressure relief valves DN200• train magnets with lost memory up to 7 TeV• cryo collimators upgrade-1• several smaller scale repairs and consolidations (leaks, belows, screens etc)

• 2014 Physics 6.5x6.5 TeV, peak luminosity 1.4 x10 33 cm-2 s-1 , integrated luminosity of ~8 fb-1

• 2015 Physics 7x7 TeV, peak luminosity 3.0 x10 33 cm-2 s-1 , integrated luminosity of ~24 fb-1

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HL LHC upgrade• 2016-2017 : SLHC Phase 1 peak luminosity up to 2 x10 34 cm-2 s-1

• Linac4 (160 MeV, H- ) or earlier 2014???• preparation for new large aperture triplets• radiation tolerant electronics/new shafts for LHC• ATLAS install 4th-pixel layer at R=3.5 cm (probably earlier in 2014), CMS new 4-

layer pixel system

• 2021: SLHC Phase 2 peak average luminosity 5.0 x10 34 cm-2 s-1

• luminosity leveling • crab cavities• large aperture triplets• PS consolidation • PSB upgrade (2 GeV injection to PS)• SPS consolidation • ATLAS and CMS install new Inner Detectors• ~10 years collecting data, total luminosity 3000 fb-1

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Conclusions

• ATLAS and CMS were ready for data at 99% level• World record of 7 TeV collision energy• ATLAS and CMS rediscovered most of the results from Tevatron• Start to be competitive with Tevatron• Collected 45 pb-1 in 2010 • Heavy ions in November -December2010 was unexpected success• In 2011 expect at least 1 fb-1 of integrated luminosity at √s =7 TeV• In 2012 expect at least 5 fb-1 of integrated luminosity at √s =7 TeV

or 8 TeV• Looking forward to 2015 to reach design energy 14 TeV and

increase in luminosity• HL LHC upgrade efforts are on the way already

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SPARES

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dE/dx in pixel detectors

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gamma gamma data driven background

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Tevatron exclusion

Black Hole Event in ATLASBH evaporates into

(q and g : leptons : Z and W : n and G : H) = (72%:11%:8%:6%:2%:1%)

(hadron : lepton) is (5 : 1) accounting for t, W, Z and H decays

S.B. Giddings, S. Thomas, Phys.Rev.D65(2002)056010

High multiplicity events

gamma

Muon

Decay of 6.1 TeV Black Hole

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Event Multiplicity

Number of Extra dimensions

2

4

6

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Reconstructed BH Mass

BH will be produced with a range of masses at LHC Mass reconstruction by Σ P of all decay products

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BH will be produced with a range of masses at LHC

Black Holes

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Multibody final states • Minv of n≥3 high pT objects• pT j et >40 GeV pT e/g >20 GeV pT μ >20 GeV E Tmiss • control region ΣpT > 300 GeV and 300 GeV < Minv < 800 GeV , MC normalized to data• signal region ΣpT > 700 GeV and Minv > 800 GeV • no deviations from Standard Model observed• σ*Acceptance < 0.34 nb at 95% CL

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Performance of missing ET

• small differences data/MC for events with jets at high pT, smearing jets in MC to get agreement• some cleaning from cosmics and beam backgrounds

pT [GeV]

Calibrated