Lepton Fakes in ~ 840 /nb

Lepton Fakes in ~ 840 /nb

26 August 2010

Intro & Selections

• Reference current ttbar selections– New: Mt < 25

• Electrons: endcap alignment correction for data, no Δη

• Data & Monte Carlo samples listed at the end

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W contribution to QCD Fake Rates

• We want to measure the rate of fake leptons from QCD in data

• Leptonic W decays will contribute to some extent– We have so far required low MET ( tcmet < 20 GeV )

to reduce the contribution from W– We now require low transverse mass also ( Mt < 25 )

• What effect does the presence of W have on the fake rate?

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Electron Fake Rates in Monte Carlo

QCD_Pt30 OnlyQCD_Pt30 + Weν

V1 Fake Rate V3 Fake RateV2 Fake Rate

Presence of W does not dominate Fake Rate - W contribution introduces some bias - QCD prevails 4

( No cuts on MET or Mt )

Muon Fake Rates in Monte Carlo

W contribution suppressed by requiring low MET and Mt - We have been requiring tcmet < 20, we now require Mt < 25 also - W domination delayed by ~10 GeV in Pt - underlying QCD Fake Rate unaffected

InclusiveMu15 + Wmunu

InclusiveMu15 + Wmunu - tcmet< 20 AND Mt < 25

InclusiveMu15

InclusiveMu15- tcmet< 20 AND Mt < 25

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Fake Rate Dominated by W

Muon Fake Rates – Comparison of Data and Monte Carlo

W evident in Data also - Good data / MC agreement - W starts to dominate above ~ 35 GeV

How do we estimate the fake rate for Pt > 35 where W is irreducible? - Simply use the fake rate from the 30-35 GeV Pt bin for Pt > 35 GeV - QCD background peaks at low Pt and QCD FR is somewhat flat - Alternatively, use fake rate from b tagged jets

Data ( HLT_Mu9 AND 15 GeV Offline Jet )MC InclusiveMu15 + WmunuMC InclusiveMu15

Luminosity ~ 840 / nb

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Fake Rates - Jet vs. Lepton Triggered

• Lepton fake rates have so far been determined from jet triggered ( HLT_Jet15U ) samples– Then require offline lepton away from jet trigger

• Jet triggers are now heavily prescaled– HLT_Jet15U prescale is now 200 ( 4.1 v3 at 3.5x1030 )

• Alternatively, can derive fake rates from lepton triggered samples ( Mu9, Ele10_LW_L1R )– Then apply threshold to offline jet away from lepton

• Lepton & Jet triggers should give the same result – Lepton triggers offer more statistics

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Electron Fake Rates in DataComparison of Jet & Lepton Triggers


HLT_Jet15UHLT_Ele10_LW_L1RAND 15 GeV Offline Jet

Jet & Lepton Triggered Fake Rates are Comparable - Lepton Triggered samples offer higher statistics


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Muon Fake Rates in DataComparison of Jet & Lepton Triggers


HLT_Jet15U

HLT_Mu9 AND15 GeV Offline Jet

Jet & Lepton Triggered Fake Rates Agree Before Run 137000 - Difference after run 137000 not yet understood - Lepton triggered samples offer higher statistics

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Runs before 137000All Runs

Jet Threshold Dependence of Lepton Fake Rates

• Systematic errors are estimated by measuring the dependence of the fake rate on the jet threshold

• Comparison of lepton triggered fake rates with different offline jet pt thresholds are shown on the following slides

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Muon Fake Rates in DataDependence on Jet Threshold


Systematics ~ 50%Isolation relaxed ( 0.15 to 0.40 ) in the muon fake rate denominator

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HLT_Mu9

5 GeV 15 GeV 30 GeV 50 GeV

Electron Fake Rates in DataDependence on Jet Threshold


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HLT_Ele10_LW_L1R 5 GeV 15 GeV 30 GeV 50 GeV

Systematics ~ 50%V2 fake rate ( which does not relax isolation) shows least dependence on jet threshold


Summary• Leptons from W decay pollute QCD fake rates

– Results in tolerable bias for electrons– Muon fake rate is dominated by W above ~ 35 GeV in

spite of requiring low MET and Mt. • Solution: Extend fake rate from lower Pt or require b tagged jets

• Fake rates derived from lepton triggers offer more statistics than those from jet triggers

• Jet Threshold– Systematics ~ 50%

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Samples• /InclusiveMu15/Spring10-START3X_V26_S09-v1/GEN-SIM-RECO• /QCD_Pt30/Spring10-START3X_V26_S09-v1/GEN-SIM-RECO • /Wenu/Spring10-START3X_V26_S09-v1/GEN-SIM-RECO• /Wmunu/Spring10-START3X_V26_S09-v1/GEN-SIM-RECO

• /MinimumBias/Commissioning10-SD_EG-Jun14thSkim_v1/RECO• /EG/Run2010A-Jun14thReReco_v1/RECO• /EG/Run2010A-Jul16thReReco-v2/RECO• /EG/Run2010A-PromptReco-v4/RECO

• /MinimumBias/Commissioning10-SD_Mu-Jun14thSkim_v1/RECO• /Mu/Run2010A-Jun14thReReco_v1/RECO• /Mu/Run2010A-Jul16thReReco-v1/RECO• /Mu/Run2010A-PromptReco-v4/RECO

• /MinimumBias/Commissioning10-SD_JetMETTau-Jun14thSkim_v1/RECO• /JetMETTau/Run2010A-Jun14thReReco_v2/RECO• /JetMETTau/Run2010A-Jul16thReReco-v1/RECO• /JetMETTau/Run2010A-PromptReco-v4/RECO

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Backup Slides

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Runs < 137000 Runs > 137000 Runs < 139000

Runs > 139000 Runs < 141000

Runs > 141000 Runs < 143000

Run Dependence of Muon Fake Rate

All Runs Runs > 136500HLT_15u

HLT_Mu9 AND 15 GeV Offline Jet

Discrepancy between Jet & Lepton triggered FR for runs>137000 not understood

Difference between Jet15U and Muon triggers at high PT?

• This was also seen earlier in the summer• The most likely explanation was that of a run

dependence– Jet15U samples the very earliest runs– Muon triggers are uniform

• We need to verify this again by making the same plots as the previous page but broken up in run periods

• Slide from this summer are in backup (as a reminder of what we had then)

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Slide circulated in an emai message by Claudio on 10 July 2010

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Electron Fake Rates in Monte Carlo

QCD_Pt30 OnlyWeν OnlyQCD_Pt30 + Weν

Numerator & Denominator Pt distributions

Num V2 DenV1 Den V3 Den

Fake Rates

QCD_Pt30 OnlyQCD_Pt30 + Weν


Presence of W does not dominate Fake Rate at high Pt 21

Muon Fake Rates in Monte Carlo

W dominates Fake Rate above ~ 25 GeV

InclusiveMu15 + WmunuInclusiveMu15Wmunu

Fake Rate DenominatorNumerator

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Muon Fake Rates – Comparison of Data and Monte Carlo

W evident in Data also- Good agreement between data and Monte Carlo - W starts to dominate above ~ 35 GeV

Data ( HLT_Mu9 AND 15 GeV Offline Jet )InclusiveMu15 + WmunuInclusiveMu15Wmunu


Fake Rate DenominatorNumerator

W Supression:- tcmet< 20 - Mt < 25

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Muon Fake Rates in DataDependence on Muon Trigger


Fake Rate stable for different Muon triggers

W Supression:- tcmet< 20 - Mt < 25

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Electron Fake Rates in DataComparison of 10 & 15 GeV Lepton Triggers


HLT_Ele10_LW_L1RHLT_Ele15_LW_L1R

W Supression: tcmet< 20, Mt < 25


25Electron 10 & 15 triggers are comparable

Electron Fake Rates in DataComparison of 10 GeV Lepton Triggers


HLT_Ele10_LW_L1RHLT_Ele10_SW_L1RHLT_Ele10_LW_EleId_L1RHLT_Ele10_SW_EleId_L1RW Supression: tcmet< 20, Mt < 25


26Trigger ID increases V1 & V2 Fake Rates

Trigger ID cancels out in V3.

V1 & V2 have no offline ID. Trigger IDdecreases the denominator, increasing the Fake Rate

Electron Fake Rates in DataComparison of 15 GeV Lepton Triggers


HLT_Ele15_LW_L1RHLT_Ele15_SW_L1RHLT_Ele15_SW_EleId_L1RHLT_Ele15_LW_CaloEleId_L1RW Supression: tcmet< 20, Mt < 25


27Trigger ID increases V1 & V2 Fake Rates

Electron Selections• ttbar: Tight Electron Selections

– Pt > 10– SC Et > 10– |η| < 2.5– ECAL Seeded– Spike Removal– VBTF 90 ID

• Data corrected for Endcap alignment• dEta cut removed

– d0 < 400 – Iso< 0.15– No muon with dR of 0.10– Conversion Rejection

• Hit Pattern• Dist < 002• Dcottheta< 002

• Loose Electron Selections– d0 removed for V1, V2, V3– V1: V2 AND V3– V2: Electron ID removed– V3: Isolation relaxed to 0.40

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Lepton Fakes in ~ 840 /nb

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