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Results Of Recent SUSY Studies At ATLAS

This presentation provides an overview of recent SUSY studies conducted at ATLAS, focusing on inclusive and exclusive signatures. The preliminary results of these studies using the mSUGRA framework are discussed, along with the selection of mSUGRA points based on experimental data. The presentation also highlights the use of effective mass and kinematic edges for estimating the SUSY mass scale.

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Results Of Recent SUSY Studies At ATLAS

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  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. 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 (m0, m1/2, A0, 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. I.Aracena SUSY 2005, Durham, UK

  3. Excluded by b s (CLEO,BELLE) Favored by gμ−2 at the 2σ level Muon g−2 coll. Focus point WMAP: 0.094<Ωχh2<0.129 Stau1=LSP Funnel region s-channel Higgs-exchange. Stau coannihilation The (m0,m1/2) - mSUGRA plane Bulk region t-channel slepton exchange. (ATL-PHYS-2004-011) (Ellis et al., Phys. B565 (2003) 176) I.Aracena SUSY 2005, Durham, UK

  4. mSUGRA points The following points in the mSUGRA space have been selected for analysis with the full ATLAS detector simulation (GEANT4). Events generated with HERWIG 6.505 (+JIMMY). SUSY spectra obtained with ISAJET7.71 All results shown in this talk are obtained from new full simulation data! I.Aracena SUSY 2005, Durham, UK

  5. p q l l 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 (Hinchliffe et al., Phys. Rev. D55 (1997) 5520): • Cuts to reject SM background • 4 jets with PT > 50GeV • 2 jets with PT > 100GeV • ET > max(0.2Meff,100GeV) • no lepton miss coannihilation ATLAS 20.6fb−1 Preliminary SUSY signal (full sim.) miss SM background (ATL-PHYS-2004-011) I.Aracena SUSY 2005, Durham, UK

  6. MSUSY vs. Effective mass • Plot MSUSY vs. the peak value of the Meff (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. • Meff can be used over a broad range of mSUGRA models. Preliminary ATLAS Meff is a good variable for the estimation of the SUSY mass scale I.Aracena SUSY 2005, Durham, UK

  7. Preliminary ATLAS Bulk region 4.20fb−1 p p • only SUSY signal (full sim.) • select events with 2 leptons 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 mll. • Remove SUSY/SM BG using OppositeFlavor/OppositeSign (OF/OS) pairs, e.g. . I.Aracena SUSY 2005, Durham, UK

  8. Dilepton distribution - coannihilation Stau coannihilation region ATLAS Preliminary ATLAS MC truth lL • two edges. • only signal events with ≥2 leptons. • Fit results: • - mll,fit (L)=(56.45±1.15)GeV • - mll,fit (R)=(102.0±0.01)GeV MC truth lR full sim. data 20.6fb−1 max max MC truth (Herwig) small BR and at least one lepton has low transverse momentum. pT(lepton) (GeV) I.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. ATLAS Preliminary 6.9fb−1 full sim. Preliminary ATLAS 6.9fb−1 • Apply following cuts to reject potential SM BG: • at least 4 jets with pT>50GeV. • at least 2 jets with pT>100GeV. • ETmiss > 100GeV. full sim. After SM cuts Shape not much affected by cuts, but reduced statistics. I.Aracena SUSY 2005, Durham, UK

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

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

  12. jet2 jet1 ATLAS 20.6fb−1 Right handed squark mass • In mSUGRA usually large . • Such events contain two hard jets and missing ET. • 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. Preliminary • Coannihilationregion • Select ≥2 jets PT>200GeV • and ET >400GeV • Use “true” value • . • True value . full sim. miss I.Aracena SUSY 2005, Durham, UK

  13. MC truth (Herwig) Bulk region Tau signatures Decay chains involving taus are challenging, due to: • Escaping neutrino. • Only consider hadronic tau decays. Distorted shape of the ditau mass distribution. 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. I.Aracena SUSY 2005, Durham, UK

  14. Reconstruct the dilepton inv. mass in the decay chain. Shape of can be calculated given knowledge of tau polarizations. Extracting polarization is challenging. mττ (vis)/98.3 Ditau mass distribution Preliminary • 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. ATLAS 4.2fb−1 full sim. mττ (vis) (GeV) Use MC truth as a first approx. and fit obtained function to data. I.Aracena SUSY 2005, Durham, UK

  15. Ditau mass distribution Stau coannihilation region at least one tau has small transverse momentum. ATLAS Preliminary full sim. 20 fb-1 OS pairs SS pairs Preliminary 8 7 6 5 4 3 2 1 0 ATLAS full sim. 13 fb-1 • 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 0 40 80 120 160 200 Mττ,vis (GeV) In both scenarios hint for an endpoint, but need more stats for fit. I.Aracena SUSY 2005, Durham, UK

  16. ATLAS Preliminary M(02) (GeV) M(01) (GeV) Reconstruct sparticle masses Perform a chi-square fit • Oism observables smeared with exp. resolution, Oi “true” observable values. • Assume 1% error on the measured observables: (Stau coannihilation region) ATLAS Preliminary M(01) (GeV) Can reconstruct mass with ~10% precision, mass diff. with ~1% I.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! I.Aracena SUSY 2005, Durham, UK

  18. BACKUP SLIDES

  19. SM background Dominant SM background processes: • Z+N jets • W+N jets • tt+N jets • multijets (QCD) • sum of all BG ATLAS TDR 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. SM cuts+1lepton I.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 GeV m(dR) = 734 GeV m(χ30) = 466 GeV m(uL) = 760 GeV m(uR) = 735 GeV m(χ20) = 264 GeV m(sL) = 765 GeV m(sR) = 734 GeV m(χ10) = 137 GeV m(cL) = 760 GeV m(cR) = 735 GeV m(b1) = 698 GeV m(b2) = 723 GeV m(t1) = 573 GeV m(b2) = 723 GeV m(eL) = 255 GeV m(eR) = 154 GeV m(stau1) = 147 GeV m(stau2) = 257 GeV σLO = 6.8pb I.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 GeV m(dR) = 3576 GeV m(χ30) = 180 GeV m(uL) = 3563 GeV m(uR) = 3574 GeV m(χ20) = 160 GeV m(sL) = 3564 GeV m(sR) = 3576 GeV m(χ10) = 103 GeV m(cL) = 3564 GeV m(cR) = 3574 GeV m(b1) = 2924 GeV m(b2) = 3500 GeV m(t1) = 2131 GeV m(t2) = 2935 GeV m(eL) = 3547 GeV m(eR) = 3547 GeV m(stau1) = 3520 GeV m(stau2) = 3534 GeV σLO = 4.9pb I.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 GeV m(dR) = 840 GeV m(χ30) = 477 GeV m(uL) = 867 GeV m(uR) = 842 GeV m(χ20) = 288 GeV m(sL) = 871 GeV m(sR) = 840 GeV m(χ10) = 150 GeV m(cL) = 867 GeV m(cR) = 842 GeV m(b1) = 717 GeV m(b2) = 779 GeV m(t1) = 642 GeV m(t2) = 798 GeV m(eL) = 412 GeV m(eR) = 351 GeV m(stau1) = 181 GeV m(stau2) = 393 GeV σLO = 4.5pb I.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 GeV m(dR) = 611 GeV m(χ30) = 464 GeV m(uL) = 632 GeV m(uR) = 612 GeV m(χ20) = 219 GeV m(sL) = 636 GeV m(sR) = 611 GeV m(χ10) = 118 GeV m(cL) = 631 GeV m(cR) = 612 GeV m(b1) = 575 GeV m(b2) = 611 GeV m(t1) = 424 GeV m(t2) = 651 GeV m(eL) = 230 GeV m(eR) = 155 GeV m(stau1) = 150 GeV m(stau2) = 232 GeV σLO = 6.8pb I.Aracena SUSY 2005, Durham, UK

  24. lepton selection cuts Cuts applied to all samples: • Electrons • pT > 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 • pT > 10 GeV, |η| < 2.5 • Reco 2< 20 • Isolation: • ET < 6 GeV in cone 0.4 I.Aracena SUSY 2005, Durham, UK

  25. Reconstruct the dilepton inv. mass in the decay chain. Dilepton distribution – Bulk region • Only SUSY signal events. • No SM background cuts. • Fit a triangular shape convoluted with a Gaussian. ATLAS 4.20fb−1 Bulk region • After SM BG cuts + 2 leptons • Loose stats but still triangular shape visible. • Fitted value after cuts: mll = (99.8±1.2)GeV ATLAS 4.37fb−1 I.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 , , . ATLAS Preliminary 6.9fb−1 No SM cuts Preliminary 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. I.Aracena SUSY 2005, Durham, UK

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

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

  29. Lepton+jets distributions - coannihilation Stau coannihilation region ATLAS 20.6 fb−1 Preliminary Use to disentangle the mlq distributions Divide mllq into mll < 58GeV and 58<mll<101GeV. mqll (GeV) mql(low) (R) ATLAS 20.6 fb−1 mql(low) (L+εR) Preliminary mql(low) (L+R) ATLAS 20.6 fb−1 Preliminary I.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 20.6 fb−1 I.Aracena SUSY 2005, Durham, UK

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

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

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