1. 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)

2. 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

3. 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

4. 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.

5. 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

6. Alan Watson, Birmingham UniversityLake Louise Winter Institute, 17-23 Feb 2002 Standard Model Higgs: Decay LEP Limit

7. 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

8. 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

9. 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

10. 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

11. 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

12. 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

13. 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 ~~

14. 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 ~~

15. 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 ~~

16. 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 ~

17. 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               

18. 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

19. 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 ~ ~ ~ ~

20. 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

21. 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…