Electron Isolation Performance

Transcription

1 Electron Isolation Performance LeBourgeois, Matthew 13th November, 2007

2 Table of Contents To date, have only shown muon isolation studies Definition of Electron Types Electron Reconstruction Electron Identification Tracker Based Isolation Methods Results Comparison to muons Calorimetry Based Isolation Methods Results Comparison to muons Summary p.2

3 Computing Details 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 /QCD_Pt_15_20/CMSSW_1_5_2-CSA /GEN-SIM-DIGI-RECO (880K events) /QCD_Pt_20_30/CMSSW_1_5_2-CSA /GEN-SIM-DIGI-RECO (480K events) /QCD_Pt_30_50/CMSSW_1_5_2-CSA /GEN-SIM-DIGI-RECO (54K events) /QCD_Pt_50_80/CMSSW_1_5_2-CSA /GEN-SIM-DIGI-RECO (520K events) /QCD_Pt_80_120/CMSSW_1_5_2-CSA /GEN-SIM-DIGI-RECO (720K events) /QCD_Pt_120_170/CMSSW_1_5_2-CSA /GEN-SIM-DIGI-RECO (1,260K events) /QCD_Pt_170_230/CMSSW_1_5_2-CSA /GEN-SIM-DIGI-RECO (450K events) /QCD_Pt_230_300/CMSSW_1_5_2-CSA /GEN-SIM-DIGI-RECO (610K events) /QCD_Pt_300_380/CMSSW_1_5_2-CSA /GEN-SIM-DIGI-RECO (1,270K events) /QCD_Pt_380_470/CMSSW_1_5_2-CSA /GEN-SIM-DIGI-RECO (870K events) /QCD_Pt_470_600/CMSSW_1_5_2-CSA /GEN-SIM-DIGI-RECO (1020K events) /QCD_Pt_600_800/CMSSW_1_5_2-CSA /GEN-SIM-DIGI-RECO (410K events) /QCD_Pt_800_1000/CMSSW_1_5_2-CSA /GEN-SIM-DIGI-RECO (550K events) p.3

4 Definition of Electron Types For this talk, define different types of electrons Standard GSF Electrons label: pixelmatchedgsfelectrons Electrons with standard medium PTDR style ID* (Endcap,Barrel) x (Golden,BigBrem,Narrow,Showering) PTDR Medium Golden BigBrem Narrow Showering Variable Barrel Endcap Barrel Endcap Barrel Endcap Barrel Endcap EoverPInMax EoverPInMin deltaetain deltaphiin HoverE E9overE EoverPOutMax EoverPOutMin deltaphiout inveminusinvp bremfraction sigmaetaetamax sigmaetaetamin sigmaphiphimax sigmaphiphimin *e.g. Ribeiro, P.: p.4

5 Definitions continued Electrons with new loose Cut-Based (CB) style ID* (Endcap,Barrel)x (bremming w/ E/p ~ 1, low brem, bad track E/p!= 1) E/p E/p fbrem Δϕ in (E/p>1.5) Δη in CUTS Variable Barrel > 0.8 > 0.2 H/E < σ ηη < Δϕ in < 0.05 < 0.09 < E seed /p in > 0.11 Loose 1 Endcap > 0.8 > 0.2 < < < 0.07 < < > 0.8 > 0.2 < 0.09 *Sani, M.: > 0 Barrel < 0.10 < < < > 0.91 Loose 2 Endcap > 0.8 > 0.2 < 0.12 < < 0.03 < < > 0.85 Barrel > 0.8 > 0.2 < < < < 0.09 < > 0.11 fbrem = (p in - p out )/p in Loose 3 Endcap > 0.8 > 0.2 < < < < < > 0 p.5

6 Validating Electron Reconstruction First use of electrons, need to check efficiency, validate. Used a H(M=170) ZZ 4e sample One studies previous cuts: Previous Studies* Denominator: MC Electrons with a corresponding SC with E T > 5 GeV Numerator**: Associated Electron with: abs(δη) < E T (GeV) H/E < 0.1 ΔR in < 0.1 σ ηη < 0.03 && (σ ηη < abs(η) > 1.479) E/p out > 0.9 eta This Study E T (GeV) Global GSF Electrons GSF Electrons *see: **see: eta p.6

7 Validation by fake comparison Used /QCD_Pt_50_80/CMSSW_1_5_2-CSA /GEN-SIM-DIGI-RECO Almost same cuts: Denominator: SC with E T > 5 GeV Numerator**: Associated Electron with: abs(δη) < H/E < 0.1 ΔR in < 0.1 σ ηη < 0.03 && (σ ηη < abs(η) > 1.479) E/p out > 0.9 *Previous Studies E T (GeV) This Study E T (GeV) Similar shapes for efficiency and fake rates, can say that we are on the correct path, moving on eta Global GSF Electrons GSF Electrons eta *see: p.7

8 GSF Electrons in DY Sample Will look at electrons with P T > 15 GeV for this isolation study There is an excess of electrons not from the Z/γ* As well as contaminations from fakes difference comes mostly from τ s p.8

9 Electrons after selection New CB selection is more efficient in selecting electrons from Z s while still maintaining a better rejection for electrons in a QCD sample. p.9

10 Tracker Based Isolation p.10

11 Tracker Based Isolation Electrons leave a simple imprint in the tracker(unlike the ECAL) Tracker isolation is more stable in multiple interaction scenarios Electrons in the tracker are theoretically similar to muons minus the contribution from conversion, if any Track Requirements P T > 1 GeV d0 < 1 mm χ 2 / dof < 10 Hits Tracker >= 8 Δdz < 5 mm p.11

12 Contribution from Conversion Compare truth matched daughters of Z/γ* electrons and muons. If no contribution from conversion, should have exact same efficiency. Seems as if there is more <ΣP T > within a ΔR cone in electrons as compared to muons For 97% efficiency in the muon sample, can only achieve 96% for electrons when comparing MC truth matched leptons In real life: For 97.0% efficiency for Global Muons one can get just over 94% for CB Loose electrons CB Loose CB Loose p.12

13 Tracker Isolation Techniques 1. Use an inner and outer cone: Sum CTF Tracks between an inner and outer cone. Efficiency curves show smaller inner cone and an outer cone close to 0.3 Chose < ΔR < 0.3 for easy comparison to muons Inner Cone Comparison CB Loose Outer Cone Comparison CB Loose CB Loose p.13

14 Tracker Isolation Techniques 2. Veto CTF tracked matched to GSF Track Use match by hits algorithm (if the tracks shared > 50%, considered a match) ~98% efficiency of matching If no match, ΣP T unaffected (nothing to sum)! CB Loose p.14

15 Tracker Isolation Techniques 3. Try to minimize effects of e eγ, γ ee by vetoing all other electrons in the cone Use same ctf-gsf matching technique CB Loose p.15

16 Comparison of Techniques All methods perform similarly Inner veto cone is simplest, and already available other techniques depend on GSF-CTF matching (assoc. map?) p.16

17 Isolation Cut Variables Compare: Number of Tracks ΣP T ΣP T /P t e Σ(P T /P Te ) 2 Here, P T e is taken from 1_5_X GSF Electron definition of a 4-Vector CB Loose Notice the variation of ΣP T /P t e and Σ(P T /P Te ) 2 over P T ΣP T seems more robust p.17

18 Isolation vs P T ΣP T < 6 give ~97% efficiency for CB Loose Electrons Plot different types of leptons for this cut value: p.18

19 Summary and Recommendations For similar lepton purity, electron isolation performance almost as good as muon isolation performance conversion not a big issue ΣP T is more robust than ΣP T / P T e Lepton Type CB Loose PTDR Medium Muons DY ee Cut Efficiency (after reco) 98.5% 88.7% - QCD Cut Efficiency (after reco) 17.0% 28.4% Z ee is for MC electrons QCD is for all reco electrons - DY Isolation Efficiency 97.1% 96.6% QCD Isolation Efficiency 15% 14% Denominator: # Leptons Numerator: w/ ΣP T < 6 (GeV) p.19

20 Calo Based Isolation p.20

21 ECAL Based Methods 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 very primitive still need to address issue of Hybrid Basic Clusters in the barrel what about pre-shower? Is there a better way? 2. Remove IBCs within a smaller cone around the position of the electron where it enters the calorimeter (the naïve approach) 3. Remove IBCs within a Δη strip around the position of the electron where it enters the calorimeter p.21

22 Prequel to Method 1 The isolation performance is very dependent on the Super Cluster algorithm performance. Unaccounted electron energy goes into the ΣE T Makes isolated electrons less isolated Is the same effect present in nonisolated electrons? Particle Gun Data Thanks to Matteo Sani: 10 GeV Generated 20 GeV Generated 30 GeV Generated GeV p.22

23 Method 1 Compare isolation in the barrel and endcap See that the barrel has a wider spread around 0. Due to summing IBC s while having hybrid SC s in the barrel Despite the BC mismatch, better isolation performance in the barrel than in the endcap. p.23

24 Method 1 Optimization Vary the outer cone to determine the best ΔR. Looks as if ΔR < 3.0 is large enough to contain the electron, whereas ΔR < 4.0 guarantees electron containment in the endcap. p.24

25 Method 2 Optimization Vary inner and outer cones to check efficiency Barrel Barrel Endcap Endcap Again, the endcap tends to need a larger ΔR, both for the inner and outer cones. p.25

26 Method 3 Optimization Vary outer cone and width of Δη strip Barrel Barrel Endcap Endcap p.26

27 Vetoed Energy Distributions Sum of the vetoed E T divided by the E T of the electron for each isolation technique Sharper peak for Method 1 Large tail to the right for Method 3 ΔR < 0.3 Strip: Δη > 0.03 Cone: ΔR > 0.07 Muons: ΔR > 0.07 DY QCD p.27

28 Barrel vs. Endcap Show all methods with comparison to muons Barrel ΔR < 0.3 Strip: Δη > 0.03 Cone: ΔR > 0.07 Muons: ΔR > 0.07 Nothing compares to muons, but Method 3 out performs Method 1. Endcap ΔR < 0.3 Strip: Δη > 0.03 Cone: ΔR > 0.07 Muons: ΔR > 0.07 p.28

29 HCAL Performance Used HCAL RecHits, with an outer and (possibly?) an inner cone. No sign of leakage. p.29

30 Combined performance Overall electrons have a poorer, but not bad, performance than muons. Some numbers (better presenation to come): 97% for DY Endcap, gives 12.3% QCD 97% for DY Barrel, gives 6.3% QCD ΔR < 0.3 ECAL Strip: Δη > 0.03 HCAL Cone: ΔR > 0 Tracker Cone: ΔR > ΔR < 0.3 ECAL Cone: Δη > 0.07 HCAL Cone: ΔR > 0.1 Tracker: Lepton Veto* p.30