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Z electron + τ Jet Search.

Z electron + τ Jet Search. Joshua Swanson. Details. Dataset: /Ztautau/Summer08_IDEAL_V11_redigi_v2/GEN-SIM-RECO CMS Version: CMSSW_2_2_13_HLT. Analysis done using PAT v2 and PF2PAT. Analysis normalized to luminosity of 1 fb -1. Background. Major sources of background for Z->e+τ jet.

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Z electron + τ Jet Search.

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  1. Z electron + τ Jet Search. Joshua Swanson Joshua Swanson

  2. Details • Dataset: /Ztautau/Summer08_IDEAL_V11_redigi_v2/GEN-SIM-RECO • CMS Version: CMSSW_2_2_13_HLT. • Analysis done using PAT v2 and PF2PAT. • Analysis normalized to luminosity of 1 fb-1. Joshua Swanson

  3. Background • Major sources of background for Z->e+τ jet. • QCD (Pythia EM Enriched sample Pt bins 20-30, 30-80, and 80-170) • W+Jets (Madgraph) • Photon+Jets (Pythia using Pt bins up to 800) • Z(ee)+Jets (Pythia) Joshua Swanson

  4. Pre-Selection • Require event passes HLT-Ele15-LW-L1R • Require reconstruction of PAT e and PF τ • Mτe>5 GeV • Require particles in the tracker fiducial volume (|eta| < 2.5) Joshua Swanson

  5. Initial Cuts • Require electron passes version 1 tight ID. • Require either 1 or 3 tracks in the signal cone. • Require the sum of the charge (τ+e) equals zero. • Apply standard e and μ discrimination for the τs. Joshua Swanson

  6. Electron Ecal Isolation • Ecal Iso: ΣRecHits in a cone centred on e SC, and “Jurassic” footprint removal, strip with specified η and inner veto cone. • Jurassic strip half width, barrel: 0.02; endcap: 0.02 • Jurassic veto cone radius, barrel: 0.045; endcap: 0.070 • RecHit noise cut, barrel: 0.08 GeV; endcap: 0.30 GeV • Cone radius: 0.4 Joshua Swanson

  7. Electron Ecal Isolation Reject Reject Endcaps Barrel Joshua Swanson

  8. Electron Track Isolation • Σpt(tracks) from center electron track vertex. • Inner veto cone radius: 0.015 • Pt threshold cut on tracks: 1.0 • Cone radius: 0.3 Reject Joshua Swanson

  9. Electron HCal Isolation • Σ(ECaloTowers) in cone centered on electron ECAL super cluster. • Cone Radius: 0.4 • Veto: None (in CMSSW 22X) Reject Joshua Swanson

  10. Electron Et • A cut on electron Et discriminates against electrons coming from Zs or Ws. Reject Joshua Swanson

  11. Tau Pt • τ pt > 22 GeV cuts out significant amounts of QCD Background. • τ pt < 60 GeV rejects high energy particles from Ws and Zs Reject Joshua Swanson

  12. Transverse mass of the e & PF MET. • A cut on the Transverse mass of the electron and PF MET discriminates against electrons coming from Ws. Reject Joshua Swanson

  13. Require the τ and e are back to back. • A cut at 2.5 and 4 in |Δϕ| seem reasonable based on Pythia MC but in real data these may need to be looser. Reject Joshua Swanson

  14. Cut on Invariant Mass of the τ and e • A cut on high visible invariant mass helps cut out Z->ee events where e are faking τs. Reject Joshua Swanson

  15. Electrons, Barrel and Endcaps only • Better ways of discriminating against QCD are needed especially in the endcaps. Sig = 380 events Bkgd = 610 events Sig = 2100 events Bkgd = 1600 events Endcaps Barrel Joshua Swanson

  16. Final Results • In the end 3.8% of the signal survives and only 0.002% of the background. • Significance (S/sqrt(S+B)) = 36 • S/B = 1.1 Sig = 2500 events Bkgd = 2300 events Joshua Swanson

  17. Conclusions • With slightly improved QCD rejection an accurate measurement of the Z->e + τ jet cross section should be available at 1 fb-1. • Looser electron selection criteria in the endcaps cause significant amounts QCD to be reconstructed as signal. • Electrons faking τs still pose a problem even with 98.5% rejection. Joshua Swanson

  18. Future Work • Work on optimizing electron selection. • Switch to the better performing shrinking cone algorithm. • Move to 3_1_X and use new Summer09 samples when available. • Develop statistically robust methods to quantify QCD background. • Develop data driven methods for estimating τ misidentification rate. Joshua Swanson

  19. Back Up Slides Joshua Swanson

  20. Electron efficiency using a V01 Tight ID • Gen Electrons (passing tight ID and matched) divided by all gen electrons. Joshua Swanson

  21. Tau Efficiencies • Gen taus (matched) divided by all gen taus. Joshua Swanson

  22. Single Electron Trigger • HLT_Ele15_LW_L1R • A single electron trigger, using the large pixel-matching window (“LW”) at HLT. • The supercluster used to seed the pixel matching must have ET > 5 GeV and H/E < 0.2. • At least one HLT electron with ET > 15 GeV is required. • No isolation is required. Joshua Swanson

  23. τ electron and μ discrimination • Electron Pre-ID is based on a fast MVA. • Standard electron τ discrimination: • E/P < 0.8 or H3X3/P > 0.15 for candidates not passing electron pre-id. • E/P < 0.95 or H3X3/P > 0.05 for candidates passing the electron pre-id. • τ is rejected as a μ if: • The leading track matches any identified μ (default), or it matches an identified μ with at least one segment in the μ chambers. Joshua Swanson

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