alan watson, birmingham university lake louise winter institute, 17-23 feb 2002 atlas physics in...

Alan Watson, Birmingham UniversityAlan Watson, Birmingham University Lake Louise Winter Institute, 17-23 Feb 20Lake Louise Winter Institute, 17-23 Feb 200202

ATLAS Physics in Year 1ATLAS Physics in Year 1

Detector and Machine ScheduleDetector and Machine Schedule

Standard Model PhysicsStandard Model Physics

Higgs Physics Higgs Physics

SUSYSUSY

(Exotics Covered Elsewhere)(Exotics Covered Elsewhere)


LHC ScheduleLHC Schedule

Current schedule:Current schedule:

Can do a lot with 10 Can do a lot with 10 “good”“good” fb fb-1-1 (well understood, (well understood, calibrated detector, well-tuned MC, etc). This may take calibrated detector, well-tuned MC, etc). This may take time though.time though.

Will concentrate here on Will concentrate here on “rapid discovery”“rapid discovery” potential potential rather than precision measurementrather than precision measurement

1/4/2006 1/4/2006 30/4/2006 30/4/2006 Pilot run: Pilot run: LL = 5 = 5101032322210103333, , 1fb 1fb11

Detector commissioningDetector commissioning

1/5/2006 1/5/2006 31/7/2006 31/7/2006 Shutdown. Continue detector installationShutdown. Continue detector installation

1/8/2006 1/8/2006 28/2/2007 28/2/2007 Physics Run: Physics Run: LL =2 =2101033 33 , 10fb, 10fb11 Continue detector commissioningContinue detector commissioning Start Physics Start Physics


Standard Model ProcessesStandard Model ProcessesMany SM studies systematically-Many SM studies systematically-limited with 10fblimited with 10fb-1-1

ProvidedProvided detector well understood! detector well understood!

First tasks:First tasks:Understand physics environmentUnderstand physics environmentMeasure Measure for W, Z, top, jets for W, Z, top, jets

–Check Parton Density Functions, Check Parton Density Functions, normalise MC generatorsnormalise MC generators

Calibrate detector:Calibrate detector:–Z Z , ee:, ee: tracker, calorimeter, tracker, calorimeter,

spectrometer calibrationspectrometer calibration–t t Wb Wb jjb: jjb: reconstruct W reconstruct W jet jet

energy calibrationenergy calibration

Very interesting SM physics will Very interesting SM physics will followfollow

W jj reconstruction in top events


Low Mass HiggsLow Mass Higgs

LEP 2 Limit

Critical Region:Critical Region:Favoured by EW dataFavoured by EW data

–mmHH < 196 GeV (95% < 196 GeV (95% CL)CL)

Required in MSSMRequired in MSSM–mmhh < 135 GeV < 135 GeV

Possible competition Possible competition from Tevatronfrom TevatronTwo mass ranges:Two mass ranges:

> ~135 GeV:> ~135 GeV: ATLAS alone sensitive with 10fb ATLAS alone sensitive with 10fb-1-1

115-130 GeV:115-130 GeV: need to combine need to combine channelschannels and and experimentsexperiments to reach 5 to reach 5 discovery. discovery.


Standard Model Higgs: ProductionStandard Model Higgs: Production

Leading order

WW/ZZ fusion

associated WH, ZH

associated ttH

gg fusion


Standard Model Higgs: DecayStandard Model Higgs: Decay

LEP Limit


qqH qqH qqWW qqWW(*)(*) qq l qq lll(1)(1)

W*

W

Recent Study:Recent Study:Signature:Signature:

–isolated dilepton (ee, isolated dilepton (ee, , e, e), p), pT T > 20 > 20 GeVGeV

–angular correlationsangular correlations

–2 tag jets > 40, 20 GeV, 2 tag jets > 40, 20 GeV, > 3.8 > 3.8

–EETTmissmiss > 30 GeV > 30 GeV

–veto on jets |veto on jets || < 3.2| < 3.2

Main backgrounds:Main backgrounds:–tt:tt: suppressed by jet cuts & vetos suppressed by jet cuts & vetos

–WW:WW: suppressed by angular cuts suppressed by angular cuts


qqH qqH qqWW qqWW(*)(*) qq l qq lll(2)(2)

mmHH (GeV) (GeV) 131300

141400

151500

161600

171700

181800

191900

Signal (10fbSignal (10fb--

11))1818 3333 5454 8888 8484 6969 4949

S/BS/B 1.21.2 1.81.8 2.92.9 4.34.3 4.04.0 3.33.3 2.22.2

Results:Results:Significance < Zeppenfeld et. al.Significance < Zeppenfeld et. al.

–lepton, tag jet efficiencieslepton, tag jet efficiencies

–both related to gluon ISR/FSRboth related to gluon ISR/FSR

Still large discovery potentialStill large discovery potential–S/B >> gg fusion WWS/B >> gg fusion WW(*)(*) channel channel

–far less reliant on background far less reliant on background modellingmodelling

Sensitivity:Sensitivity: 135-190 GeV with 135-190 GeV with 5fb5fb-1-1

Preliminary: backgrounds still under study


H H WW WW(*)(*) l lllComplementary to 4l channel:Complementary to 4l channel: BR BR 700fb. 700fb.

– Large signal, but S/B < 1Large signal, but S/B < 1

Backgrounds:Backgrounds:

– Irreducible: WWIrreducible: WW(*)(*)

– Reducible: WZ, ZZ, tt, Wt, WbbReducible: WZ, ZZ, tt, Wt, Wbb

Cuts:Cuts:

– isolated leptons, pisolated leptons, pTT > 20, 10 GeV > 20, 10 GeV

– EETTmissmiss > 40 GeV, M > 40 GeV, Mllll < 80 GeV < 80 GeV

– opening angle < 1 radianopening angle < 1 radian

– no jets Eno jets ETT > 15 GeV > 15 GeV

ResultsResults

– significant signal 160-180 GeVsignificant signal 160-180 GeV

– no mass peak. Requires precise no mass peak. Requires precise background knowledgebackground knowledge

W*

W


ATLAS100 fb-1

mH=120 GeV

MMHH < 130 GeV < 130 GeV

b

b

background large (S/B ~4%), background large (S/B ~4%), but smoothbut smooth

–use sidebands to measureuse sidebands to measure calorimeter performance calorimeter performance

crucialcrucial

–energy, angle resolutionenergy, angle resolution

– /jet, /jet, // separation separation

complex final statecomplex final state

–H H bb, t bb, t bjj, t bjj, t bl bl– fully reconstruct both topfully reconstruct both top

suppress combinatorics

–ttjj dominant backgroundttjj dominant backgroundb-tagging crucial

ttH, H ttH, H bb bbH H

Must combine these delicate measurements, & also with CMS


SM Higgs: SummmarySM Higgs: Summmary

Different RangesDifferent Ranges < 130 GeV: ttH and H< 130 GeV: ttH and H

– delicate measurementsdelicate measurements

– need to combine expts.need to combine expts.

130-190 GeV: ZZ130-190 GeV: ZZ(*)(*) & WW & WW(*)(*)

– complementary channelscomplementary channels

– 1 experiment suffices1 experiment suffices

– WW fusion channel covers WW fusion channel covers whole rangewhole range

> 2M> 2MZZ: ZZ : ZZ 4l 4l

– ““gold plated” channelgold plated” channel

– include other modes > 400 include other modes > 400 GeVGeV

WW fusion analysis not included


MSSM Higgs PotentialMSSM Higgs Potential5 contours

SM-like modes:SM-like modes:–h h tth tth ttbb; H ttbb; H 4l 4l

MSSM modes:MSSM modes:–A/H A/H ,,,tt; H ,tt; H ,cs,tb,cs,tb

–H H hh; A/H hh; A/H Zh Zh SUSY modes:SUSY modes:

–A/H A/H

h h

EnhancementsEnhancements–bbA, bbH couplingsbbA, bbH couplings–A/H A/H , , decays decays

SuppressionsSuppressions–hh generally slightly generally slightly

suppressedsuppressed–WWH, ZZH suppressedWWH, ZZH suppressed–WWA, ZZA absentWWA, ZZA absent


SuperSymmetry: OverviewSuperSymmetry: Overview

Theoretical Interest:

Gravity, Unification, Hierachy Problem

Distinctive Signatures:

Cascades of decays

Multijets, leptons & ETmiss Many Scenarios:

Different mass hierachies, decay chains, SUSY breaking models

Stable LSP? Or maybe not?

Experimental Programme:

Inclusive searches

Special Signatures

Reconstruct Decay Chains

High Rates:

Strong production of q, g~ ~


SUSY: Inclusive SearchSUSY: Inclusive Search Inclusive signature:Inclusive signature:

– 4 jets 4 jets EETT > 50 GeV, > 50 GeV, ppT1T1 > 100 > 100 GeVGeV

– EETTmissmiss > max(100 GeV, 0.2 > max(100 GeV, 0.2MMeffeff))

““effective mass” variable:effective mass” variable:

MMeffeff = = EETT + + ppT1T1 + + ppT2T2 + + ppT3T3 + + ppT4T4

Gives S/B ~ 10 at high Gives S/B ~ 10 at high MMeffeff

Estimate MEstimate MSUSYSUSY = min( = min(MMgg, , MMqq) )

with ~10% precisionwith ~10% precision

~ ~


SUSY: Observability (mSUGRA)SUSY: Observability (mSUGRA)

Different Different scenarios scenarios studiedstudied

All observable All observable (>5(>5) with 10fb) with 10fb11

Sensitive to q/g Sensitive to q/g masses > 2 TeVmasses > 2 TeV

Reach limited by Reach limited by , not detailed , not detailed detector detector performanceperformance

~ ~


Special Signals (GMSB)Special Signals (GMSB)

Long-lived Long-lived 1100 GG

Count non-pointing Count non-pointing Exploit longitudinal Exploit longitudinal

segmentation of ATLAS segmentation of ATLAS ECALECAL

~~

Long-lived Long-lived RR

Use Use spectrometer to spectrometer to measure TOF measure TOF mass mass

Ratio of events with 2/1 Ratio of events with 2/1 detected NLSP detected NLSP lifetimelifetime

~


llll Signatures Signatures

ll l l

ll

~

~~

Point 5: m m = 111

GeV(no background subtraction)

Select events using Select events using MMeffeff, E, ETTmissmiss

Like-sign, opposite charge Like-sign, opposite charge dileptonsdileptons

Subtract background: Subtract background: eeeeeeFirst precise First precise measurement?measurement?Could be, if BF significantCould be, if BF significant

Alternatively: Alternatively: h h


Other Other decays decays

~ ~

~

significant if kinematically significant if kinematically allowedallowed

may be the h discovery channelmay be the h discovery channel

may dominate at large may dominate at large tantan

neutrinos smear edgeneutrinos smear edge

h h

bbbb

~ ~

10 fb10 fb-1 -1 endpoint endpoint 3GeV3GeV


Further ReconstructionFurther Reconstruction

Other information:Other information: Rates, kinematic distributionsRates, kinematic distributions

Can only start this Can only start this programme:programme:

But we can make a startBut we can make a start

Lepton-jet combinations:Lepton-jet combinations: If see dilepton edge, work back If see dilepton edge, work back

up the chain:up the chain:

e.g. qe.g. qLL q q l lRR l l q q

l l l l q q

constraints:constraints: l lll endpoint, l endpoint, lq q edge, ledge, lllq endpointq endpoint

3 constraints3 constraints on on 4 masses4 masses

~~ ~ ~


~~

SUSY: SummarySUSY: Summary

Discovery “straightforward”Discovery “straightforward” Inclusive analyses very effectiveInclusive analyses very effective

Simple estimates of g/q mass scale work wellSimple estimates of g/q mass scale work well

SUSY parameters are the challengeSUSY parameters are the challenge Reconstruct decay chains Reconstruct decay chains masses masses

– Main background = other SUSY processesMain background = other SUSY processes

Measure branching fractionsMeasure branching fractions

Objectives: SUSY parameters, SUSY-breaking Objectives: SUSY parameters, SUSY-breaking scale/mechanismscale/mechanism

Big job:Big job: will keep us busy for a while will keep us busy for a while


Summary Summary Higgs Searches:Higgs Searches:

– Good prospectsGood prospects over range favoured by LEP data over range favoured by LEP data– Observing Higgs < 130 GeV in year 1 Observing Higgs < 130 GeV in year 1 delicatedelicate and and

demandingdemanding SUSY:SUSY:

– Should observe if Should observe if MMSUSYSUSY < 2 TeV < 2 TeV– Understanding Understanding what sort of SUSY will be a large job!what sort of SUSY will be a large job!

Many other interesting searches I’ve not covered:Many other interesting searches I’ve not covered:– See See Ambreesh Gupta’sAmbreesh Gupta’s talk talk

Depends on understanding of detector/environment Depends on understanding of detector/environment – huge efforthuge effort will be needed to make some of these studies will be needed to make some of these studies

possiblepossible Whatever (if anything) we find in year 1, Whatever (if anything) we find in year 1, it will only be it will only be

the beginning…the beginning…

alan watson, birmingham university lake louise winter institute, 17-23 feb 2002 atlas physics in...

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