1. Results Of Recent SUSY Studies At ATLAS Ignacio Aracena University of Bern On behalf of the ATLAS collaboration SUSY 2005 July 18 – 23, 2005, IPPP Durham, UK Outline Introduction Inclusive SUSY Signatures Exclusive Signatures - leptons (electrons, muons) - taus Conclusions

2. July 22th 2005I.Aracena SUSY 2005, Durham, UK 2 Introduction Preliminary results of recently produced full simulated data with the initial layout of the ATLAS detector. Analyzed SUSY signatures in the mSUGRA (RPC) framework (m 0, m 1/2, A 0, tanβ, sgn(μ)). Selected mSUGRA points chosen according to recent experimental data (WMAP,LEP limits,CLEO,BELLE). The material shown here is the result of a collaboration-wide effort over the past six months and is a summary of what has been shown at the ATLAS Physics Workshop in June 2005.

3. July 22th 2005I.Aracena SUSY 2005, Durham, UK 3 Funnel region s-channel Higgs-exchange. The (m 0,m 1/2 ) - mSUGRA plane WMAP: 0.094<Ω χ h 2 <0.129 Excluded by b s  (CLEO,BELLE) Favored by g μ −2 at the 2σ level Muon g−2 coll. Stau1=LSP (Ellis et al., Phys. B565 (2003) 176) Bulk region t-channel slepton exchange. (ATL-PHYS-2004-011) Stau coannihilation Focus point

4. July 22th 2005I.Aracena SUSY 2005, Durham, UK 4 mSUGRA points M 0 (GeV)M 1/2 (GeV)A0A0 tanβsgn(μ)m top (GeV) Coannihilation70350010+175 Focus point3550300010+175 Funnel region320375050+175 Bulk (ATL-PHYS-2004-011) 100300-3006+175 Scan130-6000600,1000010+175 low mass point200160-40010+175 The following points in the mSUGRA space have been selected for analysis with the full ATLAS detector simulation (GEANT4). All results shown in this talk are obtained from new full simulation data! Events generated with HERWIG 6.505 (+JIMMY). SUSY spectra obtained with ISAJET7.71

5. July 22th 2005I.Aracena SUSY 2005, Durham, UK 5 Inclusive SUSY signatures A typical SUSY event at LHC will contain hard jets + n leptons and large missing transverse energy, E T. The SUSY mass scale: The effective Mass gives a handle on the SUSY mass scale (Hinchliffe et al., Phys. Rev. D55 (1997) 5520): Cuts to reject SM background –4 jets with P T > 50GeV –2 jets with P T > 100GeV –E T > max(0.2M eff,100GeV) –no lepton q l l p ATLAS 20.6fb −1 SM background (ATL-PHYS-2004-011) SUSY signal (full sim.) miss Preliminary miss coannihilation

6. July 22th 2005I.Aracena SUSY 2005, Durham, UK 6 M SUSY vs. Effective mass Plot M SUSY vs. the peak value of the M eff (from full simulation). Repeat this for different mSUGRA models. Correlation line from previous fast simulation analysis, Hinchliffe et al., Phys. Rev. D55,D. Tovey, Phys. Lett. B498 (2001) 1. M eff can be used over a broad range of mSUGRA models. M eff is a good variable for the estimation of the SUSY mass scale ATLAS Preliminary

7. July 22th 2005I.Aracena SUSY 2005, Durham, UK 7 Exclusive signatures After initial discovery of SUSY the measurement of the sparticle masses will be the next step. Two invisible LSP in each event, so no direct mass measurement possible. Obtain kinematic edges from invariant mass distributions of involved particles, e.g. dilepton distribution m ll. Remove SUSY/SM BG using OppositeFlavor/OppositeSign (OF/OS) pairs, e.g.. p p ATLAS Bulk region 4.20fb − 1 Preliminary only SUSY signal (full sim.) select events with 2 leptons

8. July 22th 2005I.Aracena SUSY 2005, Durham, UK 8 two edges. only signal events with ≥2 leptons. Fit results: - m ll,fit (L)=(56.45±1.15)GeV - m ll,fit (R)=(102.0±0.01)GeV max Dilepton distribution - coannihilation MC truth (Herwig) ATLAS small BR and at least one lepton has low transverse momentum. MC truth l L MC truth l R full sim. data 20.6fb −1 ATLAS Preliminary p T (lepton) (GeV) Stau coannihilation region

9. July 22th 2005I.Aracena SUSY 2005, Durham, UK 9 Dilepton distribution – focus point Focus point heavy scalars, no slepton in decay. direct 3-body decay: dilepton distribution gives mass diff. between,,. only signal events with ≥2 leptons. 6.9fb −1 ATLAS Apply following cuts to reject potential SM BG: at least 4 jets with p T >50GeV. at least 2 jets with p T >100GeV. ETmiss > 100GeV. After SM cuts Shape not much affected by cuts, but reduced statistics. ATLAS Preliminary full sim. 6.9fb −1

10. July 22th 2005I.Aracena SUSY 2005, Durham, UK 10 Combine the two leptons with the two hardest jets in the event: Leptons+jets distributions - m llq p p Obtain more edges: include the quark coming from the squark decay ATLAS 4.20fb − 1 ATLAS 4.20fb − 1 Preliminary 0 200 400 600 800 1000 16 12 8 4 0 Entries/10Gev 0 200 400 600 800 1000 60 50 40 30 20 10 0 Entries/10Gev Bulk region: signal evts (full sim.); ≥2 jets and 2 leptons. Apply OF/OS subtraction. full sim. m llq (GeV) small m llq (GeV) large

11. July 22th 2005I.Aracena SUSY 2005, Durham, UK 11 Take the jet used for and compute m lq using each of the two leptons (Allanach et al., JHEP 0009 (2000) 004): Leptons+jets distributions - m lq(low), m lq(high) p p Stau coannihilation region ATLAS full sim. 20.6 fb − 1 Preliminary M lq(low) (GeV) ATLAS full sim. 20.6 fb − 1 Preliminary M lq(high) (GeV) ≥2 jets/leptons, subtract OF/OS pairs.

12. July 22th 2005I.Aracena SUSY 2005, Durham, UK 12 Right handed squark mass In mSUGRA usually large. Such events contain two hard jets and missing E T. Estimate the mass using the stranverse mass, (Lester et al., Phys.Lett.B463 (1999) 99): Take from dilepton and dilepton+jet measurements. If is known, is obtained from the endpoint of the distribution. jet1 jet2 Coannihilation region Select ≥2 jets P T >200GeV and E T >400GeV Use “true” value. True value. ATLAS 20.6fb −1 Preliminary miss full sim.

13. July 22th 2005I.Aracena SUSY 2005, Durham, UK 13 And they are particularly interesting: Non-negligible Yukawa coupling. for large tanβ, decays into have large BR. Can use tau polarization measurement to further constrain the underlying SUSY model. Tau signatures Decay chains involving taus are challenging, due to: Escaping neutrino. Only consider hadronic tau decays. Distorted shape of the ditau mass distribution. Bulk region MC truth (Herwig)

14. July 22th 2005I.Aracena SUSY 2005, Durham, UK 14 Ditau mass distribution Bulk region select events with two reconstructed taus. Uncorrelated pairs accounted for by using same-sign pairs. True endpoint Endpoint structure visible at the expected value. Shape of can be calculated given knowledge of tau polarizations. Extracting polarization is challenging. Reconstruct the dilepton inv. mass in the decay chain. ATLAS 4.2fb −1 full sim. Preliminary m ττ (vis) (GeV) m ττ (vis) /98.3 Use MC truth as a first approx. and fit obtained function to data.

15. July 22th 2005I.Aracena SUSY 2005, Durham, UK 15 Ditau mass distribution full sim. 20 fb -1 Stau coannihilation region at least one tau has small transverse momentum. Funnel region no lepton mass edge: Select events with ≥2 taus and: ≥4 jets with pT>50GeV; ≥1 jet pT>100GeV ETmiss ≥ max(100GeV,0.2Meff) OS pairs SS pairs full sim. 13 fb -1 OS pairs SS pairs ATLAS 0 40 80 120 160 200 876543210876543210 ATLAS Preliminary M ττ,vis (GeV) In both scenarios hint for an endpoint, but need more stats for fit.

16. July 22th 2005I.Aracena SUSY 2005, Durham, UK 16 Reconstruct sparticle masses Perform a chi-square fit O i sm observables smeared with exp. resolution, O i “true” observable values. M(  0 1 ) (GeV) Assume 1% error on the measured observables: Can reconstruct mass with ~10% precision, mass diff. with ~1% (Stau coannihilation region) ATLAS Preliminary M(  0 1 ) (GeV) ATLAS Preliminary M(  0 2 ) (GeV)

17. July 22th 2005I.Aracena SUSY 2005, Durham, UK 17 Conclusions New studies of mSUGRA signatures using new full simulation data of the ATLAS detector have been shown. Various experimentally challenging points in the mSUGRA parameter space in agreement with recent experimental data have been chosen. If SUSY exists at the TeV scale, ATLAS should be able to observe clean inclusive signatures above the SM background. Lots of techniques exist / are being developed to assess the sparticle masses and the underlying model parameters. Many exclusive studies can be carried out with few fb −1 of data, i.e. ~ 1 year at low luminosity. There are still many things to be studied more carefully (acceptance, calibration, trigger, SM BG,…). Analyses of this new full simulation data have just started. There is still a lot we can learn from this before first collisions in 2007!

18. BACKUP SLIDES

19. July 22th 2005I.Aracena SUSY 2005, Durham, UK 19 SM background Dominant SM background processes: Z+N jets W+N jets tt+N jets multijets (QCD) sum of all BG Previous studies are based on Parton shower. New SM BG estimation using ME generator (ALPGEN 1.33) W/Z + N jets, tt + N jets are generated and processed with the fast ATLAS simulation Collinear and soft kinematic regions are assessed with PS (PYTHIA). MLM method used for ME-PS matching. ATLAS TDR SM cuts+1lepton

20. July 22th 2005I.Aracena SUSY 2005, Durham, UK 20 Coannihilation point – mass spectrum m0 = 70; m1/2 = 350; A0 = 0; tanβ=10; μ>0 m(g) = 832 GeV m(dL) = 765 GeVm(dR) = 734 GeVm(χ30) = 466 GeV m(uL) = 760 GeVm(uR) = 735 GeVm(χ20) = 264 GeV m(sL) = 765 GeVm(sR) = 734 GeVm(χ10) = 137 GeV m(cL) = 760 GeVm(cR) = 735 GeV m(b1) = 698 GeVm(b2) = 723 GeV m(t1) = 573 GeVm(b2) = 723 GeV m(eL) = 255 GeVm(eR) = 154 GeV m(stau1) = 147 GeVm(stau2) = 257 GeV σ LO = 6.8pb

21. July 22th 2005I.Aracena SUSY 2005, Durham, UK 21 Focus point – mass spectrum m0 = 3550; m1/2 = 300; A0 = 0; tanβ=10; μ>0 m(g) = 857 GeV m(dL) = 3564 GeVm(dR) = 3576 GeVm( χ3 0) = 180 GeV m(uL) = 3563 GeVm(uR) = 3574 GeVm( χ 20) = 160 GeV m(sL) = 3564 GeVm(sR) = 3576 GeVm(χ10) = 103 GeV m(cL) = 3564 GeVm(cR) = 3574 GeV m(b1) = 2924 GeVm(b2) = 3500 GeV m(t1) = 2131 GeVm(t2) = 2935 GeV m(eL) = 3547 GeVm(eR) = 3547 GeV m(stau1) = 3520 GeVm(stau2) = 3534 GeV σ LO = 4.9pb

22. July 22th 2005I.Aracena SUSY 2005, Durham, UK 22 Funnel region – mass spectrum m0 = 320; m1/2 = 375; A0 = 0; tanβ=50; μ>0 m(g) = 895 GeV m(dL) = 871 GeVm(dR) = 840 GeVm( χ3 0) = 477 GeV m(uL) = 867 GeVm(uR) = 842 GeVm( χ 20) = 288 GeV m(sL) = 871 GeVm(sR) = 840 GeVm(χ10) = 150 GeV m(cL) = 867 GeVm(cR) = 842 GeV m(b1) = 717 GeVm(b2) = 779 GeV m(t1) = 642 GeVm(t2) = 798 GeV m(eL) = 412 GeVm(eR) = 351 GeV m(stau1) = 181 GeVm(stau2) = 393 GeV σ LO = 4.5pb

23. July 22th 2005I.Aracena SUSY 2005, Durham, UK 23 Bulk region – mass spectrum m0 = 100; m1/2 = 300; A0 = -300; tanβ=6; μ>0 m(g) = 717 GeV m(dL) = 636 GeVm(dR) = 611 GeVm( χ3 0) = 464 GeV m(uL) = 632 GeVm(uR) = 612 GeVm( χ 20) = 219 GeV m(sL) = 636 GeVm(sR) = 611 GeVm(χ10) = 118 GeV m(cL) = 631 GeVm(cR) = 612 GeV m(b1) = 575 GeVm(b2) = 611 GeV m(t1) = 424 GeVm(t2) = 651 GeV m(eL) = 230 GeVm(eR) = 155 GeV m(stau1) = 150 GeVm(stau2) = 232 GeV σ LO = 6.8pb

24. July 22th 2005I.Aracena SUSY 2005, Durham, UK 24 lepton selection cuts Cuts applied to all samples: Electrons p T > 10 GeV, |η| < 2.5 Isolation: 4 GeV in cone 0.2 eWeight/(eWeight+piWeight) > 0.95 0.8 < E/p < 1.3 in barrel 0.7 < E/p < 2.5 in endcap Muons p T > 10 GeV, |η| < 2.5 Reco  2 < 20 Isolation: E T < 6 GeV in cone 0.4

25. July 22th 2005I.Aracena SUSY 2005, Durham, UK 25 Dilepton distribution – Bulk region Only SUSY signal events. No SM background cuts. Fit a triangular shape convoluted with a Gaussian. Bulk region ATLAS 4.20fb − 1 After SM BG cuts + 2 leptons Loose stats but still triangular shape visible. Fitted value after cuts: m ll = (99.8±1.2)GeV Reconstruct the dilepton inv. mass in the decay chain. ATLAS 4.37fb − 1

26. July 22th 2005I.Aracena SUSY 2005, Durham, UK 26 Dilepton distribution – focus point Focus point heavy scalars, no slepton in decay. direct 3-body decay: Dilepton distribution gives mass diff. between,,. 6.9fb −1 No SM cuts ATLAS After SM cuts only few events survive: dominant SUSY production is but only survive SM cuts. 6.9fb −1 After SM cuts Endpoint structure visible, but too little stats available. ATLAS Preliminary

27. July 22th 2005I.Aracena SUSY 2005, Durham, UK 27 Lepton+jets signatures Combine two leptons with the two hardest jets in the event: : combination with the larger inv. mass. : combination with the smaller inv. mass. ATLAS 4.20fb − 1 bulk region Can use combinations of leptons and jets to constrain the sparticle mass spectrum. ATLAS 4.20fb − 1 bulk region

28. July 22th 2005I.Aracena SUSY 2005, Durham, UK 28 Take the jet used for and compute m lq using each of the two leptons (JHEP 0009 (2000) 004): Apply OF/OS subtraction Leptons+jets distributions - m lq(near), m lq(far) p p ATLAS 4.20fb − 1 bulk region ATLAS 4.20fb − 1 bulk region Preliminary

29. July 22th 2005I.Aracena SUSY 2005, Durham, UK 29 Lepton+jets distributions - coannihilation m qll (GeV) Stau coannihilation region m ql(low) (R) m ql(low) (L+εR) m ql(low) (L+R) ATLAS 20.6 fb − 1 Use to disentangle the m lq distributions Divide m llq into m ll < 58GeV and 58<m ll <101GeV. Preliminary

30. July 22th 2005I.Aracena SUSY 2005, Durham, UK 30 Lepton+jets distributions - coannihilation Move up in the decay chain: Combine the leptons with jets ATLAS coannihilation ATLAS coannihilation 20.6 fb − 1

31. July 22th 2005I.Aracena SUSY 2005, Durham, UK 31 Ditau mass distribution Funnel region no lepton mass edge: Select events with ≥2 taus full sim. 13 fb -1 OS pairs SS pairs ATLAS Preliminary

32. July 22th 2005I.Aracena SUSY 2005, Durham, UK 32 The ATLAS detector

33. July 22th 2005I.Aracena SUSY 2005, Durham, UK 33 The ATLAS initial layout Staged components: One Pixel layer Transition Radiation Tracker outer end-caps Cryostat gap scintillator Part of Muon drift tubes and half cathode strip layers Part of forward shielding Part of LAr read-out Large part of trigger/DAQ CPUs