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

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 GeV below the Z peak, but EWK group experts suggested to explore the DY mass spectrum upto kinematic limit ~ 700 GeV. 7/13/2009

List of Data Samples used 1. /Zmumu M20/Summer08 IDEAL V11 redigi v1/GEN-SIM-RECO 2. /WJets-madgraph/Summer08 IDEAL V11 redigi v1/AODSIM 3./Ztautau M20/Summer08 IDEAL V11 redigi v1/AODSIM 4. /TTJets-madgraph/Fall08 IDEAL V11 redigi v10/GEN-SIM-RECO 5./QCD BCtoMu Pt20/Summer08 IDEAL V11 redigi v1/GEN-SIM-RECO 6./QCD BCtoMu Pt30to50/Summer08 IDEAL V11 redigi v1/GEN-SIMRECO 7./QCD BCtoMu Pt50to80/Summer08 IDEAL V11 redigi v2/GEN-SIMRECO 8./QCD BCtoMu Pt80to120/Summer08 IDEAL V11 redigi v1/AODSIM 9. /QCD BCtoMu Pt120to170/Summer08 IDEAL V11 redigi v1/AODSIM 10./QCD BCtoMu Pt170/Summer08 IDEAL V11 redigi v1/AODSIM 11. /ZZ/Summer08 IDEAL V11 redigi v1/AODSIM 12. /WZ incl/Summer08 IDEAL V11 redigi v1/AODSIM 13./WW/Summer08 IDEAL V11 redigi v1/AODSIM 14./DYmumuM6to40/Summer08_PYTHIA_STARTUP_V5_redigi_v2/GEN-SIM-RECO 3LHC Physcis meeting

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

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

Online Selection:  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% 6LHC Physcis meeting Produced by Purdue group!!

LHC Physcis meeting7 Offline Selection (1): atleast two global muons in the event. QCD hadronic process is very dominating in the low mass region. Invariant mass of dimuon system after Trigger and 2 global muon selection.

LHC Physcis meeting8  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 meeting9 Efficiency of pt and eta cut : Signal = 81%, QCD = 4%, Wjets = 8% Invariant mass of dimuons after pt and acceptance cut

LHC Physcis meeting10 Selection (3) : Muon ID selection : (recommended by Muon POG ) Normalized chi2 of both leading muons < 10. Number of valid hits > 11. |d0μ 1 + d0μ 2 | < 0.01 mm for both leading muons.

LHC Physcis meeting11 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. |d0μ 1 + d0μ 2 | for two leading global muons in the event.

LHC Physcis meeting12 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 meeting13 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/pt μ and absolute isolation variable is ∑pt of tracks.  For a given signal efficiency, relative isolation variable has more background rejection as compared to absolute one. Delta R = 0.3 Delta R = 0.4

 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 ∑p T /p T    optimized  in delta R = 0.4 Veto cone of 0.01 to exclude muon tracks Only tracks with pT > 1 GeV 14LHC Physcis meeting

15  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. Selection (5) : Both muons must be if opp charge. (6) : Angle between two muons must > 2.25 rad

LHC Physcis meeting16 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 meeting17 Relative Efficiencies of all selection cuts

LHC Physcis meeting18 No of events after each selection cut expected for 100 pb -1

LHC Physcis meeting19 No of events expected in each mass bin for 100 pb -1 Total signal events = and total background expected for 100 pb -1 = 730

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. 20LHC Physcis meeting

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LHC Physcis meeting22 Absolute efficiencies of all selection cuts