drell-yan study in cms at 10 tev, with 100 pb -1 monika jindal k.mazumdar, d. bourilkov, j.b. singh...

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 20- 80 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/AODSIM11. /ZZ/Summer08 IDEAL V11 redigi v1/AODSIM12. /WZ incl/Summer08 IDEAL V11 redigi v1/AODSIM13./WW/Summer08 IDEAL V11 redigi v1/AODSIM14./DYmumuM6to40/Summer08_PYTHIA_STARTUP_V5_redigi_v2/GEN-SIM-RECO


Generation Information


XX

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) }


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%


Produced byPurdue group!!

LHC Physcis meeting 7

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.


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.


Efficiency of pt and eta cut : Signal = 81% , QCD = 4% , Wjets = 8%

Invariant mass of dimuons after pt and acceptance cut


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.


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.


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


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.

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 ∑pT/pT

optimizedin delta R = 0.4

• Veto cone of 0.01 to exclude muon tracks• Only tracks with pT > 1 GeV



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


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.


Relative Efficiencies of all selection cuts


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


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

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.


Back up


Absolute efficiencies of all selection cuts

drell-yan study in cms at 10 tev, with 100 pb -1 monika jindal k.mazumdar, d. bourilkov, j.b. singh...

Documents