A Update on Electron Isolation

Transcription

1 A Update on Electron Isolation Matthew LeBourgeois Vivek Sharma UCSD Group Meeting 5th February, 2008

2 Table of Contents To date, have shown muon isolation studies As well as preliminary electron isolation studies: Today, updates on electron isolation studies Tracker Based Isolation Updated data samples comparison to previous results comparison to muons Bug fix in Secondary Electron Algorithm Calorimetry Based Isolation Updated data samples comparison to previous results comparison to muons New Jurassic Method Summary and Recommendations p.2

3 Electron Types Considered and Data Samples For this talk, define different types of electrons Standard GSF Electrons ( pixelmatchedgsfelectrons ) Previously showed electrons with medium PTDR selection Electrons with new loose Cut-Based (CB) Selection (Endcap,Barrel)x(bremming w/ E/p ~ 1, low brem, bad track E/p!= 1) Will use CB Loose Selection for this Talk Samples are all CSA 07 simulated with 1_5_2 Ran with CMSSW_1_6_7 Drell-Yan (DY) /DrellYan_ll_40/CMSSW_1_5_2-CSA /GEN-SIM-DIGI-RECO (800K events) QCD - Weighted by LO cross section /QCD_Pt_30_50/CMSSW_1_5_2-CSA /GEN-SIM-DIGI-RECO (1.1M events) /QCD_Pt_50_80/CMSSW_1_5_2-CSA /GEN-SIM-DIGI-RECO (912K events) /QCD_Pt_80_120/CMSSW_1_5_2-CSA /GEN-SIM-DIGI-RECO (1.2M events) /QCD_Pt_120_170/CMSSW_1_5_2-CSA /GEN-SIM-DIGI-RECO (1.2M events) /QCD_Pt_170_230/CMSSW_1_5_2-CSA /GEN-SIM-DIGI-RECO (931K events) /QCD_Pt_230_300/CMSSW_1_5_2-CSA /GEN-SIM-DIGI-RECO (784K events) /QCD_Pt_300_380/CMSSW_1_5_2-CSA /GEN-SIM-DIGI-RECO (1.2M events) /QCD_Pt_380_470/CMSSW_1_5_2-CSA /GEN-SIM-DIGI-RECO (1.2M events) /QCD_Pt_470_600/CMSSW_1_5_2-CSA /GEN-SIM-DIGI-RECO (1.3M events) /QCD_Pt_600_800/CMSSW_1_5_2-CSA /GEN-SIM-DIGI-RECO (602K events) /QCD_Pt_800_1000/CMSSW_1_5_2-CSA /GEN-SIM-DIGI-RECO (729K events) p.3

4 Electron P T Distributions in DY Sample Will look at electron candidates with P T > 15 GeV for this isolation study In DY, there is an excess of electrons not from the Z/γ* Did not filter Z ττ As well as contaminations from fakes Bug fix in EID (fixed in CutBasedElectronID.cc from tag ) Contamination in QCD went from 81% to 73% Selection Efficiency for Z ee went from 97.3% to 96.9% All Electrons CB Loose MC Matched Not Matched All Electrons CB Loose MC Matched p.4

5 Tracker Based Isolation p.5

6 Track Quality Cuts Previous electron tracker isolation did not require quality cuts on the GSF Track However, GSF Tracks have fairly similar distributions to the CTF tracks P T ele > 15 GeV GSF Track Requirements d0 < 1mm χ 2 / dof < 10 Hits Tracker >= 8 CTF Track Requirements P T > 1 GeV d0 < 1 mm χ 2 / dof < 10 Hits Tracker >= 8 Δdz < 5 mm CTF Tracks for Z µµ GSF Tracks for Z ee Could cut harder on Δdz and d0, but prefer to leave loose for early data scenarios p.6

7 Dealing with the electron footprint 1. Inner cone method: Sum all tracks within a ΔR cone around the electron candidate, while vetoing cones within a smaller ΔR cone. 2. Veto candidate track: Sum all tracks within a ΔR cone around the electron candidate, while vetoing the track that belongs to the electron candidate. 3. Veto all electron tracks: Sum all tracks within a ΔR cone around the electron candidate, while vetoing all tracks belonging to electrons p.7

8 Update: Extra Electron Removal Method Algorithmic mistake in previous presentation which led to incorrect extra electron matching. Incorrect loop variable, was not matching against extra electrons New plots show more extra electrons within cone for the DY sample Before Bug FIx CB Loose After Bug Fix Before Bug Fix After Bug Fix p.8

9 Quantifying extra electron s in cone Want to know where all the extra electrons are coming from in the DY sample, and whether or not we want to remove them. A majority come from Z s, i.e. are the other leg of the DY decay. Want to remove these anyway! 23: Z 11: Electron < ΔR < 0.3 Overflow: 421: D : Δ - 521: B : Δ + p.9

10 ΔR of closest track as isolation variable Plot DR of closest track to the electron Again, add track quality cuts, to ensure track is coming from the same vertex. Remove matched electron track and all other tracks which match to electrons as in previous slides Not as powerful as ΣP T QCD DY Efficiency w/ cut on ΔR > 0.08: DY: 97% QCD 50-80: 39% p.10

11 Comparison of Veto Techniques Bug fix seems to decrease the performance of the Extra Electron Removal Method Due to the removal of unwanted tracks in QCD? DR < 0.3, w/out bug fix DR < 0.3, with bug fix Need to apply same rigorous selection to the extra electrons so an not to remove fake electrons in the QCD sample p.11

12 Efficiency curves with weighted QCD Overall performance has decreased due to the addition of the QCD PT_30-50 sample. Still seems as if there is no need to stray from inner cone method Similar performance Simplest implementation p.12

13 Summary of Tracker Isolation Inner cone method is easiest to implement, and gives the best isolation performance for signal versus background. For similar lepton purity, electron isolation performance almost as good as muon isolation performance CB Loose Electrons DY Isolation Efficiency* QCD Isolation Efficiency* ΣP T < 2 GeV ΣP T < 3 GeV ΣP T < 4 GeV ΣP T < 5 GeV ΣP T < 6 GeV ΣP T < 4 GeV (Muons) *0.015 < ΔR < % 96.1% 97.2% 97.9% 98.3% 98.2% 14.6% 19.5% 25.0% 29.8% 34.6% 28.6% p.13

14 Calo Based Isolation p.14

15 Previous Electron Footprint Removal in ECAL Sum the E T of Island Basic Clusters (IBCs) within a ΔR cone using the following methods to veto the footprint of the electron: 1. Subtract out the raw SC energy (SuperCluster Subtraction (SCS) Method) 2. Remove IBCs within a smaller cone around the position of the electron where it enters the calorimeter (the naïve approach) (Cone Method) 3. Remove IBCs within a Δη strip around the position of the electron where it enters the calorimeter (Strip Method) SCS Cone Strip p.15

16 Super Cluster Subtraction Method Compare isolation in the barrel and endcap Fixed algorithm, now match HSC to a ISC and use ISC energy to subtract out energy Performance in the endcap unaffected, but better performance in the barrel than previously. p.16

17 New algo comparison to endcap Comparison of performance in the endcap to the barrel p.17

18 New footprint removal technique - Jurassic New method to try in this pass. Combination of both the cone and strip method. Called Jurassic not because it was implemented in ORCA, but because it is shaped like the sign in Jurassic Park ΔR ΔR in Δη Combine the cone and strip method to get the Jurassic Method Cone Strip Jurassic p.18

19 Optimizing Jurassic Method Vary inner Δη strip, inner ΔR cone, and outer ΔR cone Choose: Δη > < ΔR < 0.4 p.19

20 ECAL electron isolation comparison Compare all four techniques with new QCD weighting. New Jurassic method slightly outperforms the SC matching method, and the strip method. Cone method still lacks the ability to capture the electron footprint, and hence performs worse. ΔR < 0.4 Cone: ΔR > 0.07 Strip: Δη > 0.03 Jurassic: Δη > 0.01, ΔR > 0.05 CB Loose Electrons ΣE T < 2 GeV ΣE T < 3 GeV ΣE T < 4 GeV ΣE T < 5 GeV DY Isolation Efficiency* 91.7% 95.5% 97.1% 97.9% QCD Isolation Efficiency* 25.8% 35.1% 43.5% 51.4% *w/ Jurassic Method, Barrel p.20

21 Combined tracker and calorimeter performance Combine ECAL, HCAL and tracker Isolation Should be a high correlation between the HCAL isolation and the tracker isolation See a slight performance increase by adding the HCAL ΔR < 0.4 Tracker: ΔR > ECAL: Δη > 0.01, R < 0.05 HCAL: ΔR > 0.0 CB Loose Electrons ΣE T < 6 GeV ΣE T < 8 GeV ΣE T < 10 GeV ΣE T < 12 GeV *Barrel DY Isolation Efficiency* 93.2% 95.8% 97.1% 97.9% QCD Isolation Efficiency* 7.45% 11.9% 17.0% 22.6% p.21

22 Summary and To Do Added new algorithm to ECAL isolation - Jurassic Updated samples with full range of QCD samples Would like to add vertex compatibility Need to optimize track quality cuts to better reflect current state of affairs in tracking Add electron ID to extra vetoed electrons within cone p.22