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Update on searches for ZZ signal in the 3 electron channel

LO. Update on searches for ZZ signal in the 3 electron channel. Azeddine Kasmi Bob Kehoe Many Thanks to: David , Pavel, Julia. NLO. OUTLINE. A search for the non-resonant ZZ signal in the ZZ3e channel was carried out.

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Update on searches for ZZ signal in the 3 electron channel

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  1. LO Update on searches for ZZ signal in the 3 electron channel Azeddine Kasmi Bob Kehoe Many Thanks to: David , Pavel, Julia NLO

  2. OUTLINE • A search for the non-resonant ZZ signal in the ZZ3e channel was carried out. • Pt, ETmiss, Isolation and Z mass cuts were used to reduce the WZ, ttbar, and Zbb backgrounds. • The signal efficiencies and background rejections will be shown • Conclusion and Future Plan

  3. PT of ElectronsZbb (left) ZZ (right)

  4. PT of ElectronsWZ (left) ttbar (right)

  5. Signal and Background after Pt cuts

  6. Signal + Background (scaled) Zbb3l Omitted ttbar WZ ZZ

  7. ETmiss in signal and Background ETmiss WZ ttbar Zbb ZZ M3e

  8. ETmiss in signal and Backgroundvs M3e ETmiss WZ ttbar ZZ ETmiss Zbb M3e M3e

  9. Pt cut & ETmiss < 20 GeV Zbb Omitted ZZ ttbar WZ

  10. Signal Efficiency and Background Rejection of ETmiss

  11. So far • ET miss is a good cut to reduce the WZ and ttbar background • Further background reduction needs to be done • Zbb  3l remains dominant

  12. Signal and Background after Pt cuts & ETmiss

  13. Isolation • The electrons from ZZ should be isolated unlike the electrons from Zbb • Etcone 30 cut may be used to discriminate the Zbb

  14. IsolationEtcone/Et in case of Zbb (left) ZZ (right) b electron Cut on 0.2

  15. IsolationEtcone/Et in case of ttbar (left) WZ (right)

  16. Pt cut & ETmiss < 20 GeV & etcone/et <0.2 ZZ WZ ttbar Zbb

  17. Signal and Background after Pt cuts & ETmiss & Isolation

  18. Use Z mass as a cut e2 Z • Find which combination of 2 electrons makes a Z for both samples ZZ and Zbb • Define a variable Z_Best which takes the closest invariant mass to PDG Z of 1&3 or 2&3 • This Z_Best will be used to distinguish between ZZ and Zbb e4 e3 e1 e1 Z Z e2 b b

  19. Mz12 (left) && Z_Best (right) Zbb_Mz12 (not scaled) ZZ_Mz12 Zbb_Z_Best (not scaled) ZZ_Z_Best

  20. Mz12 vs Mz_Best Zbb ZZ

  21. Pt cut & ETmiss < 20 GeV & etcone/et <0.2|MzPDG – Z_Best| < 20 GeV Sig_eff = 51 % Bkg_rej = 94% Bkg:sig = 30:1

  22. Z_Best vs Isolation ZZ Zbb This shows the M_ZBest as a function of the isolation of the 3rd leading electron in both cases ZZ and Zbb.

  23. Pt cut & ETmiss < 20 GeV & Isolation on 3rd leading electron < 0.1|MzPDG – Z_Best| < 10 GeV Sig_eff = 40 % Bkg_rej = 98% Bkg:sig = 15:1

  24. Conclusion && Future Plan • The ETmiss is good in case of WZ and ttbar background. • Zbb was reduced considerably but still not enough. • Looking for another cut to reduce Zbb is crucial. • Cut on jets: the Zbb event has two leading jets from the b-quarks give some discrimination power • Try to find the 4th candidate electron to use it to find the second Z peak • Optimize the cuts • Try the analysis for L= 1 fb-1 - 10 fb-1 • Higher statistics for ttbar

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