Data Driven study for Same Sign Dileptons July 31 st 2009, “CMS SUSY Leptonic Meeting” 1 Sanjay Padhi

Introduction Same sign dileptons associated with high pt jets and large MET allows efficient suppression of the SM backgrounds should be sensitive to new (non-SM) physics Study same sign dileptons in ee, e  and  modes Lepton p T : 20/10 GeV, |  | < 2.4 High Missing E T Large Jet Activity Focus on reducing and measuring SM backgrounds New method to address Charge mis-measurement (Charge flips) Fake Leptons (Same method as used in previous study, WW, tt) _ July 31 st 2009, “CMS SUSY Leptonic Meeting” 2 Sanjay Padhi

Event Selection - I Trigger: HLT_Ele15_SW_L1R.OR. HLT_Mu9 Lepton p T : 20/10 GeV, |  | < 2.4 Id & Isolation (See backup slides) No explicit 3 rd lepton veto is used Z-veto if extra lepton in the event: - makes a Z with one of the candidate leptons (suppresses WZ ) Charge flip rejection (this talk) Track Corrected MET (tcMET) is used as a measure for MET L2L3 corrected SisCone – 0.5 CaloJets Pt > 30 GeV, |  | < 2.4 July 31 st 2009, “CMS SUSY Leptonic Meeting” 3 Sanjay Padhi

Event Selection - II - tcMET > 80 GeV – Eliminates DY & Wjets - Njets > 2 && SumJetPt > 200 GeV – Eliminates (almost) everything else Note: No attempt has been made to optimize these cuts. Log scale: tcMET Log scale: sumJetPt Njet Additional Cuts: Before Njets, SumJet & tcMET cuts After tcMET cuts, No Jet cuts July 31 st 2009, “CMS SUSY Leptonic Meeting” 4 Sanjay Padhi

Study Charge mis-reconstruction using electron gun sample Cut to eliminate electrons with Charge flips: Associate GSF to GeneralTracks (CTF) using hit sharing Veto electrons if: charge of GSF Track != charge of associated CTF Aside on: Reducing Charge flip contributions July 31 st 2009, “CMS SUSY Leptonic Meeting” 5 Sanjay Padhi

Aside on: Reducing Charge flip contributions Reduce the Charge Mis-Id by factor – 3.9 while reducing efficiency by 2.1% For details see: July 31 st 2009, “CMS SUSY Leptonic Meeting” 6 Sanjay Padhi

Event yield table using 100pb -1 The dominant SM contribution is from top SingleTop After all cuts: July 31 st 2009, “CMS SUSY Leptonic Meeting” 7 Sanjay Padhi

Discussion of dominant background - Top \ee \\mu\\mu \e\\mu \all\\mu\\mu Total Baseline: \ee \\mu\\mu \e\\mu \all\\mu\\mu Total Baseline: \ee \\mu\\mu \e\\mu \all\\mu\\mu Total Baseline: \ee \\mu\\mu \e\\mu \all\\mu\\mu Total Baseline: \ee \\mu\\mu \e\\mu \all\\mu\\mu Total Baseline: Two leptons from top: – one with sign flip at reco level - Use Charge flip estimation One Lepton from W and Other from Heavy flavor decay or fakes - Use fake rate method to estimate the contribution a) b) c) July 31 st 2009, “CMS SUSY Leptonic Meeting” 8 Sanjay Padhi

Same sign dileptons from top – classification based on MC truth Top is the dominant background Breakdown of ttbar same sign sources Type -I: Flip sign from real W-lepton Type-II: One lepton from W and other from heavy flavor sources (b/c) One lepton from W and other from a fake lepton Type-III: Both leptons are NOT from W and are fakes Dominant contribution within Type-II is from heavy flavor sources 1 event in this table corresponds to ~23 MC events Estimate using Fake rate method July 31 st 2009, “CMS SUSY Leptonic Meeting” 9 Sanjay Padhi

Estimation of Charge flip (Type-I) contribution Overview: Use data driven Z  ee method to validate the MC within the kinematic range covered by the Z boson. Use large MC single electron gun to determine charge flip rate as function of  and pt Cover the entire pt and  range of the ttbar Details in upcoming POG presentation, note in preparation  Use the “validated” MC to predict the charge-flip in data July 31 st 2009, “CMS SUSY Leptonic Meeting” 10 Sanjay Padhi

Estimation of Charge flip (Type-I) contribution Charge flip probability as a function of |  |: - Data driven prediction (Z- based) * Single Electron gun (MC based) - MC truth - Data driven method from Z - MC Truth on Z events * Electron Gun |||| Charge flip probability July 31 st 2009, “CMS SUSY Leptonic Meeting” 11 Sanjay Padhi

Estimation of Charge flip (Type-I) contribution Additional check on ttbar: Test method with loose cuts: MET cut removed No Jet cuts Charge flip prediction and observation using 100 pb -1 Observed: 2.4 +/- 0.3 Predicted: 2.1 July 31 st 2009, “CMS SUSY Leptonic Meeting” 12 Sanjay Padhi

Estimation of fakes/heavy flavor (Type-II) events Same method as used in PAS notes – EWK & TOP Details documented in Analysis Note – CMS AN-2009/041 Measure lepton fake probability in independent jet trigger samples - Define “loose lepton” as the denominator - Define “tight lepton” as the numerator - More details on selection cuts in backup slides Apply to sample of interest July 31 st 2009, “CMS SUSY Leptonic Meeting” 13 Sanjay Padhi

Measuring Lepton Fake (Type-II) Contribution X-Check of fake rate prediction on top sample without MET & Jet cuts Type-II part of the MC Only (e  contribution): - one of the lepton is truth tagged - the other lepton is considered as “fake” or heavy flavor (HF) fake Muons Muons: Observed = 2.4 +/- 0.3 Predicted = 2.7 Electrons Electrons: Observed = 2.1 +/- 0.3 Predicted = 2.9 Yield scaled to 100 pb -1, Errors are due to MC statistics July 31 st 2009, “CMS SUSY Leptonic Meeting” 14 Sanjay Padhi

Prediction and Observation for top using 100 pb -1 Observed in top sample – (table from Slide 10) : Observed in top sample – (table from Slide 10) : Predict each components using Charge flip and Lepton fake rates: Predict each components using Charge flip and Lepton fake rates:  Using flip rate  Using fake rate Note: 1 event in this table corresponds to 23 MC events July 31 st 2009, “CMS SUSY Leptonic Meeting” 15 Sanjay Padhi

Prediction and Observation for SM using 100 pb -1 Observed: Predicted: SingleTop SingleTop Need to consider rare SM processes such as: W + W + /W - W -, ttW, VVV (V = Z, W) etc. Prediction and Observation agree to within 30% July 31 st 2009, “CMS SUSY Leptonic Meeting” 16 Sanjay Padhi

Prediction and Observation for SM + SUSY using 100 pb -1 Apply both data driven background estimation methods to combination of SM+SUSY samples to derive the prediction Then compare observed with predicted to look for excess in “signal” over the total background. July 31 st 2009, “CMS SUSY Leptonic Meeting” 17 Sanjay Padhi

Conclusions New data driven methods for reducing and estimating charge flips -x 4 reduction in electron charge flip Applied lepton fake & lepton charge flip data driven techniques on same sign Showed sensitivity within 100 pb -1 for SUSY - LM points July 31 st 2009, “CMS SUSY Leptonic Meeting” 18 Sanjay Padhi

Backup slides

Appendix – Electron ID Conversion removal: dist (2D distance at the point where the tracks are parallel) && Cot  < 0.02

Appendix SisCone – 0.5 CaloJets with L2L3 corrected: Njet > 2, SumPt > 200 GeV Track corrected MET (tcMET) > 80 GeV Jet/MET Muon-ID

Denominator used for Electron Fake Rates Electrons Pt > 10 GeV, |eta| < 2.4 No Muons within dR = 0.1 Isolation (as defined earlier) < 0.4 H/E < 0.2 Conversion rejection (as defined earlier) Veto electrons if charge of generalTrack != GSF Charge Electron-ID (category based mentioned earlier).

Denominator used for Muon Fake Rates Muons Both global and tracker muons Pt > 10 GeV, |eta| < 2.4  2 /ndof < 20 Muon isolation (defined earlier) < 0.4 |d0| < 200 microns (Corrected for beam spot, from silicon fit)

Dataset used /QCDpt30_Summer08_IDEAL_V11_redigi_v1-SingleLepton /QCDpt80_Summer08_IDEAL_V11_redigi_v1-SingleLepton

Assumed Cross sections

Data set processed using CMSSSW 2_2_10+