Slide 1 Status Report

Slide 2 QCD and W+jets Background Estimation Using Fake Rate Method Norbert Neumeister, Hwidong Yoo Purdue University EXO non-hadronic meeting January 30, 2014

Slide 3 Outline

Slide 4 Introduction

Slide 5 QCD Background (1) Use fake rate method (data-driven method) –Estimate QCD, W+jets contributions –Event which pass loose selection criteria are reweighted to predict the distribution of events which pass full selection cuts –Use single muon spectrum –Parameterize pt and eta of muons Fake Rate = N(muons) passing tight iso / N(muons) passing loose iso –Tight iso: rel. trk iso < 0.1 –Loose iso: rel. trk iso < 0.4 Cross check all methods with no iso cut as a denominator There is large EWK contamination on the single muon spectrum –DY, ttbar, diboson etc.

Slide 6 Fake Rate Fake rate in QCD MC sample No significant different on the fake rate between single muon events and dimuon events in both isolation category Inclusive Loose iso

Slide 7 EWK Contamination: pT Single muon spectrom in 2012 data There is large contamination from EWK muons These EWK muons affect the fake rate measured in data Inclusive Loose iso Tight iso

Slide 8 EWK Contamination: Eta Single muon spectrom in 2012 data There is large contamination from EWK muons These EWK muons affect the fake rate measured in data Inclusive Loose iso Tight iso

Slide 9 QCD Background (2) Several methods are used to cross check Ratio method –Remove EWK contamination from the fake rate using the ratio of QCD to EWK events in MC –Sensitive to the accuracy of the MC simulation of QCD –Fr = Fake Rate * p(QCD|tight iso)/p(QCD|loose iso) Subtraction method –EWK contaminations are predicted from MC and subtracted from the numerator and denominator event count –This method is sensitive to the accuracy of the EWK cross section and trigger algorithms used for MC simulation –Fr = (N(muons)_tight iso – EWK_tight iso (NLO))/ (N(muons)_loose iso – EWK_loose iso (NLO)) Not much different from the technique used in DY Developing macros for two methods

Slide 10 Fake Rate: Inclusive Similar results between two methods No significant dependency on the pt distribution Fit on pol0 and use as a constant

Slide 11 Fake Rate: Loose Iso Similar results between two methods No significant dependency on the pt distribution Fit on pol0 and use as a constant

Slide 12 Fake Rate: Inclusive Large dependency is found in eta distribution Nonnegligible difference between two methods Need to apply the parameterized fake rate using the muon eta

Slide 13 Fake Rate: Loose Iso Large dependency is found in eta distribution Nonnegligible difference between two methods Need to apply the parameterized fake rate using the muon eta

Slide 14 Event Weight Event weight is determined using the fake rate Ratio method, subtraction method –Weight = p(pass tight iso)/ p(fail tight, pass loose iso) = Fr / (1 – Fr) Events in which both muons fail tight isolation cut but pass loose (or inclusive) isolation cut –Weight these events to calculate QCD background

Slide 15 QCD Background Candidate Data distribution on the candiate events Inclusive Loose iso Same Sign Opposite Sign

Slide 16 Same Sign QCD Background Use constant fake rate from pt distribution Statistical uncertainty only

Slide 17 Opposite Sign QCD Background Use constant fake rate from pt distribution Statistical uncertainty only

Slide 18 Systematic Uncertainty

Slide 19 W+Jets Background Use candidate events that one muon fails tight isolation but both muons pass loose (or inclusive) isolation Apply fake rate weight factor to the candidates events Large contamination from DY and ttbar events after the selection –Subtract the MC predictions from data to take into account the contamination Opposite Sign Loose Isolation Fake rate from ratio method Opposite Sign Loose Isolation Fake rate from subtract method

Slide 20 Same Sign W+Jets Background No significant difference between two methods Statistical uncertainty only Inclusive Loose iso

Slide 21 Opposite Sign W+Jets Background No significant difference between two methods Statistical uncertainty only Inclusive Loose iso

Slide 22 Summary