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Drell-Yan study in CMS at 10 TeV, with 100 pb -1

Drell-Yan study in CMS at 10 TeV, with 100 pb -1. Monika Jindal K.Mazumdar, D. Bourilkov , J.B. Singh. LHC Physcis meeting. 1. Motivation LEP and Tevatron experiments have established Electroweak part of Standard Model very well.

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Drell-Yan study in CMS at 10 TeV, with 100 pb -1

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  1. Drell-Yan study in CMS at 10 TeV, with 100 pb-1 Monika Jindal K.Mazumdar, D. Bourilkov , J.B. Singh LHC Physcis meeting 1

  2. Motivation • LEP and Tevatron experiments have established Electroweak part • of Standard Model very well. • Confirmation of SM will be done at LHC using theoretically • well- understood processes like, Drell-Yan events (least amount • of QCD uncertainty). • With 100 pb-1 at 10 TeV, we can establish offline performance of • the detector and re-discover the SM from the low masses to the • kinematic limit; PDFs can also be tested at LHC in 100 pb -1 • scenario. • Earlier we had started exploring the DY low mass spectrum 20- • 80 GeV below the Z peak, but EWK group experts suggested to • explore the DY mass spectrum upto kinematic limit ~ 700 GeV.

  3. List of Data Samples used 1. /Zmumu M20/Summer08 IDEAL V11 redigi v1/GEN-SIM-RECO • /WJets-madgraph/Summer08 IDEAL V11 redigi v1/AODSIM • /Ztautau M20/Summer08 IDEAL V11 redigi v1/AODSIM • 4. /TTJets-madgraph/Fall08 IDEAL V11 redigi v10/GEN-SIM-RECO • /QCD BCtoMu Pt20/Summer08 IDEAL V11 redigi v1/GEN-SIM-RECO • /QCD BCtoMu Pt30to50/Summer08 IDEAL V11 redigi v1/GEN-SIMRECO • /QCD BCtoMu Pt50to80/Summer08 IDEAL V11 redigi v2/GEN-SIMRECO • /QCD BCtoMu Pt80to120/Summer08 IDEAL V11 redigi v1/AODSIM • 9. /QCD BCtoMu Pt120to170/Summer08 IDEAL V11 redigi v1/AODSIM • /QCD BCtoMu Pt170/Summer08 IDEAL V11 redigi v1/AODSIM • /ZZ/Summer08 IDEAL V11 redigi v1/AODSIM • /WZ incl/Summer08 IDEAL V11 redigi v1/AODSIM • /WW/Summer08 IDEAL V11 redigi v1/AODSIM • /DYmumuM6to40/Summer08_PYTHIA_STARTUP_V5_redigi_v2/GEN-SIM-RECO LHC Physcis meeting 3

  4. Generation Information X X • InclusivePPMuX has large scaling factor for 100 pb -1 and • InclusiveMuPt15 has large pt cut on muons. LHC Physcis meeting 4

  5. PAT Filter used to select events with atleast two muons: {minLayer1Muons = cms.EDFilter("PATMuonMinFilter",     src = cms.InputTag("selectedLayer1Muons"),     minNumber = cms.uint32(2) } LHC Physcis meeting 5

  6. Online Selection: Produced by Purdue group!! • Single Muon Trigger : HLT_Mu9 (single muon with pt > 9 GeV) • Double Muon Trigger : HLT_DoubleMu3 (2 muons pT > 3 GeV) • OR of single muon and dimuon trigger has better signal efficiency. Efficiency: Signal = 91%, Ztautau = 34%, Wjets=46%, ttjets = 54%, QCD = 23% LHC Physcis meeting 6

  7. Offline Selection (1): atleast two global muons in the event. Invariant mass of dimuon system after Trigger and 2 global muon selection. QCD hadronic process is very dominating in the low mass region. LHC Physcis meeting 7

  8. Selection 2 (a): pt of 2 leading muons > 10 GeV, 2(b): both muons must have |eta| < 2.4 Since the muons coming from heavy meson decays in QCD are relatively softer , so a pt cut > 10 is quite effective in reducing a large fraction of QCD. LHC Physcis meeting 8

  9. Invariant mass of dimuons after pt and acceptance cut Efficiency of pt and eta cut : Signal = 81% , QCD = 4% , Wjets = 8% LHC Physcis meeting 9

  10. Selection (3) : Muon ID selection : (recommended by Muon POG ) • Normalized chi2 of both leading muons < 10. • Number of valid hits > 11. • |d0μ1+ d0μ2| < 0.01 mm for both leading muons. LHC Physcis meeting 10

  11. Signal muons: transverse impact parameter is expected to be • very small . But, for decay in flight muons coming from QCD impact parameter will be larger. • Muon POG recommends a cut on |d0| to be < 0.2 mm for • prompt muons. But d0 requires the knowledge of beam spot • position! At start up beam spot position may not be known very accurately . ==>Sum of transverse impact parameter is independent of the knowledge of the beam spot position . |d0μ1+ d0μ2| for two leading global muons in the event. LHC Physcis meeting 11

  12. Optimization plot for sum of transverse impact parameter of two leading muons • Table shows the comparison of two variables. Since the behavior of two variables is almost same so it is better to choose Sum IP. • Sum IP has been optimized to be < 0.01cm LHC Physcis meeting 12

  13. Selection (4): Isolation Condition (Tracker based) • Comparison of Relative and absolute tracker isolation variable in two • different cone sizes 0.3 and 0.4 • Relative Isolation variable is defined as ∑pt/ptμ and absolute isolation variable is ∑pt of tracks. Delta R = 0.4 Delta R = 0.3 • For a given signal efficiency , relative isolation variable has more • background rejection as compared to absolute one. LHC Physcis meeting 13

  14. Comparison of relative Isolation variable in two cone sizes 0.3 & 0.4 • Relative Isolation variable gives more background rejection for a given signal efficiency in cone size 0.4 Isolation Variable ∑pT/pT optimized in delta R = 0.4 • Veto cone of 0.01 to exclude muon • tracks • Only tracks with pT > 1 GeV LHC Physcis meeting 14

  15. Selection (5) : Both muons must be if opp charge. (6) : Angle between two muons must > 2.25 rad • Signal muons most of the time will be back to back. So the value • for the angle between two muons has been optmized to be • > 2.25 rad. LHC Physcis meeting 15

  16. Invariant mass of dimuon system after all selection cuts After all selection cuts QCD is quite under control . Backgrounds have been reduced to a good extent keeping a good signal significance over backgrounds. LHC Physcis meeting 16

  17. Relative Efficiencies of all selection cuts LHC Physcis meeting 17

  18. No of events after each selection cut expected for 100 pb -1 LHC Physcis meeting 18

  19. No of events expected in each mass bin for 100 pb -1 Total signal events = 47563 and total background expected for 100 pb -1 = 730 LHC Physcis meeting 19

  20. Conclusions/Plans • Methods for efficient signal selection and background rejection have been • developed. • Various selection cut has been optimized to reduce backgrounds to good extent. • QCD mainly contributes to low Mll region, in high Mll region QCD is quite under control. • We are working for an analysis NOTE with CMSSW_2_2_X and will start soon • with CMSSW_3_1_X. LHC Physcis meeting 20

  21. Back up

  22. Absolute efficiencies of all selection cuts LHC Physcis meeting 22

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