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Alan Watson, Birmingham University Lake Louise Winter Institute, 17-23 Feb 2002 ATLAS Physics in Year 1 Detector and Machine Schedule Standard Model Physics Higgs Physics SUSY (Exotics Covered Elsewhere)
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Alan Watson, Birmingham UniversityLake Louise Winter Institute, 17-23 Feb 2002 LHC Schedule Current schedule: Can do a lot with 10 “good” fb -1 (well understood, calibrated detector, well-tuned MC, etc). This may take time though. Will concentrate here on “rapid discovery” potential rather than precision measurement 1/4/2006 30/4/2006 Pilot run: L = 5 10 32 2 10 33, 1fb 1 Detector commissioning 1/5/2006 31/7/2006 Shutdown. Continue detector installation 1/8/2006 28/2/2007 Physics Run: L =2 10 33, 10fb 1 Continue detector commissioning Start Physics
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Alan Watson, Birmingham UniversityLake Louise Winter Institute, 17-23 Feb 2002 Standard Model Processes Many SM studies systematically-limited with 10fb -1 Provided detector well understood! First tasks: Understand physics environment Measure for W, Z, top, jets – Check Parton Density Functions, normalise MC generators Calibrate detector: – Z , ee: tracker, calorimeter, spectrometer calibration – t Wb jjb: reconstruct W jet energy calibration Very interesting SM physics will follow W jj reconstruction in top events
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Alan Watson, Birmingham UniversityLake Louise Winter Institute, 17-23 Feb 2002 Low Mass Higgs LEP 2 Limit Critical Region: Favoured by EW data – m H < 196 GeV (95% CL) Required in MSSM – m h < 135 GeV Possible competition from Tevatron Two mass ranges: > ~135 GeV: ATLAS alone sensitive with 10fb -1 115-130 GeV: need to combine channels and experiments to reach 5 discovery.
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Alan Watson, Birmingham UniversityLake Louise Winter Institute, 17-23 Feb 2002 Standard Model Higgs: Production Leading order WW/ZZ fusion associated WH, ZH associated ttH gg fusion
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Alan Watson, Birmingham UniversityLake Louise Winter Institute, 17-23 Feb 2002 Standard Model Higgs: Decay LEP Limit
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Alan Watson, Birmingham UniversityLake Louise Winter Institute, 17-23 Feb 2002 qqH qqWW (*) qq l l (1) W*W* W Recent Study: Signature: – isolated dilepton (ee, , e ), p T > 20 GeV – angular correlations – 2 tag jets > 40, 20 GeV, > 3.8 – E T miss > 30 GeV – veto on jets | | < 3.2 Main backgrounds: – tt: suppressed by jet cuts & vetos – WW: suppressed by angular cuts
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Alan Watson, Birmingham UniversityLake Louise Winter Institute, 17-23 Feb 2002 qqH qqWW (*) qq l l (2) m H (GeV) 130140150160170180190 Signal (10fb -1 ) 18335488846949 S/B1.21.82.94.34.03.32.2 Results: Significance < Zeppenfeld et. al. – lepton, tag jet efficiencies – both related to gluon ISR/FSR Still large discovery potential – S/B >> gg fusion WW (*) channel – far less reliant on background modelling Sensitivity: 135-190 GeV with 5fb -1 Preliminary: backgrounds still under study
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Alan Watson, Birmingham UniversityLake Louise Winter Institute, 17-23 Feb 2002 H WW (*) l l H WW (*) l l Complementary to 4l channel: BR 700fb. – Large signal, but S/B < 1 Backgrounds: – Irreducible: WW (*) – Reducible: WZ, ZZ, tt, Wt, Wbb Cuts: – isolated leptons, p T > 20, 10 GeV – E T miss > 40 GeV, M ll 40 GeV, M ll < 80 GeV – opening angle < 1 radian – no jets E T > 15 GeV Results – significant signal 160-180 GeV – no mass peak. Requires precise background knowledge W*W* W
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Alan Watson, Birmingham UniversityLake Louise Winter Institute, 17-23 Feb 2002 ATLAS 100 fb -1 m H =120 GeV M H < 130 GeV b b background large (S/B ~4%), but smooth – use sidebands to measure calorimeter performance crucial – energy, angle resolution – /jet, / separation complex final state – H bb, t bjj, t bl – H bb, t bjj, t bl – fully reconstruct both top suppress combinatorics – ttjj dominant background b-tagging crucial ttH, H bb H Must combine these delicate measurements, & also with CMS
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Alan Watson, Birmingham UniversityLake Louise Winter Institute, 17-23 Feb 2002 SM Higgs: Summmary Different Ranges < 130 GeV: ttH and H – delicate measurements – need to combine expts. 130-190 GeV: ZZ (*) & WW (*) – complementary channels – 1 experiment suffices – WW fusion channel covers whole range > 2M Z : ZZ 4l – “gold plated” channel – include other modes > 400 GeV WW fusion analysis not included
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Alan Watson, Birmingham UniversityLake Louise Winter Institute, 17-23 Feb 2002 MSSM Higgs Potential 5 contours SM-like modes: – h tth ttbb; H 4l MSSM modes: – A/H , ,tt; H ,cs,tb – H hh; A/H Zh SUSY modes: – A/H – h Enhancements – bbA, bbH couplings – A/H , decays Suppressions – h generally slightly suppressed – WWH, ZZH suppressed – WWA, ZZA absent
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Alan Watson, Birmingham UniversityLake Louise Winter Institute, 17-23 Feb 2002 SuperSymmetry: Overview Theoretical Interest: Gravity, Unification, Hierachy Problem Distinctive Signatures: Cascades of decays Multijets, leptons & E T miss 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 ~~
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Alan Watson, Birmingham UniversityLake Louise Winter Institute, 17-23 Feb 2002 SUSY: Inclusive Search Inclusive signature: – 4 jets E T > 50 GeV, p T1 > 100 GeV – E T miss > max(100 GeV, 0.2M eff ) “effective mass” variable: M eff = E T + p T1 + p T2 + p T3 + p T4 Gives S/B ~ 10 at high M eff Estimate M SUSY = min(M g, M q ) with ~10% precision ~~
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Alan Watson, Birmingham UniversityLake Louise Winter Institute, 17-23 Feb 2002 SUSY: Observability (mSUGRA) Different scenarios studied All observable (>5 ) with 10fb 1 Sensitive to q/g masses > 2 TeV Reach limited by , not detailed detector performance ~~
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Alan Watson, Birmingham UniversityLake Louise Winter Institute, 17-23 Feb 2002 Special Signals (GMSB) Long-lived 1 0 G Count non-pointing Exploit longitudinal segmentation of ATLAS ECAL ~ ~ Long-lived R Use spectrometer to measure TOF mass Ratio of events with 2/1 detected NLSP lifetime ~
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Alan Watson, Birmingham UniversityLake Louise Winter Institute, 17-23 Feb 2002 l l Signatures l l l ~ ~ ~ Point 5: m m = 111 GeV (no background subtraction) Select events using M eff, E T miss Like-sign, opposite charge dileptons Subtract background: e e e First precise measurement? Could be, if BF significant Alternatively: h
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Alan Watson, Birmingham UniversityLake Louise Winter Institute, 17-23 Feb 2002 Other decays ~ ~ ~ significant if kinematically allowed may be the h discovery channel may dominate at large tan neutrinos smear edge h bb bb ~ ~ 10 fb -1 endpoint 3GeV
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Alan Watson, Birmingham UniversityLake Louise Winter Institute, 17-23 Feb 2002 Further Reconstruction Other information: Rates, kinematic distributions Can only start this programme: But we can make a start Lepton-jet combinations: If see dilepton edge, work back up the chain: e.g. q L q l R l q l l q constraints: l l endpoint, l q edge, l l q endpoint 3 constraints on 4 masses ~ ~ ~ ~
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Alan Watson, Birmingham UniversityLake Louise Winter Institute, 17-23 Feb 2002 ~~ SUSY: Summary Discovery “straightforward” Inclusive analyses very effective Simple estimates of g/q mass scale work well SUSY parameters are the challenge Reconstruct decay chains masses – Main background = other SUSY processes Measure branching fractions Objectives: SUSY parameters, SUSY-breaking scale/mechanism Big job: will keep us busy for a while Big job: will keep us busy for a while
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Alan Watson, Birmingham UniversityLake Louise Winter Institute, 17-23 Feb 2002 Summary Higgs Searches: – Good prospects over range favoured by LEP data – Observing Higgs < 130 GeV in year 1 delicate and demanding SUSY: – Should observe if M SUSY < 2 TeV – Understanding what sort of SUSY will be a large job! Many other interesting searches I’ve not covered: – See Ambreesh Gupta’s talk Depends on understanding of detector/environment – huge effort will be needed to make some of these studies possible Whatever (if anything) we find in year 1, it will only be the beginning…
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