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Outline

Outline. b-tagging methods b-tagging and high p T processes b-tagging performance at LHC Effects of efficiency and alignment on b-tagging Initial detector limitation at LHC start-up Conclusions. a 0 >0. a 0 <0. P rimar y vertex. Secondary Vertex. y. x. Space b-tagging.

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Outline

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  1. Outline • b-tagging methods • b-tagging and high pT processes • b-tagging performance at LHC • Effects of efficiency and alignment on b-tagging • Initial detector limitation at LHC start-up • Conclusions A.Rozanov TEV4LHC BNL 4 February 2005

  2. a0>0 a0<0 Primary vertex Secondary Vertex y x Space b-tagging Efficiency of b-jet tagging εb Rejection of light jets (udscg) Rj = 1./εi Jet axis B A.Rozanov TEV4LHC BNL 4 February 2005

  3. Impact parameters σ(z0) ≈120 μm σ(a0) ≈11 μm Transverse (2D) 3DMethod Longitudinal (+1D) A.Rozanov TEV4LHC BNL 4 February 2005

  4. Normalized Impact Parameter Smoothed distributions Probability density functions b(S) and u(S) jet weight : A.Rozanov TEV4LHC BNL 4 February 2005

  5. Space and vertex b-tagging Jet weight SVX energy fraction N(2 track SVX) SVX mass A.Rozanov TEV4LHC BNL 4 February 2005

  6. t b b-tagging for standard model • Studies of top physics with t-> bW • top mass • top cross-section • top polarization g incl=833 pb Rate ~ 2.5x106 evts /year j W- j υ W+ * : ℓ = e ou µ t ℓ+ g b sélect this jet Calibration of b-tagging with tt events A.Rozanov TEV4LHC BNL 4 February 2005

  7. 5s MH(GeV) b-tagging for SM Higgs b-tagging role in: • Discovery channel • ttH with H-> bb • Supplementary channels • WH with H-> bb • ttH with H-> WW* • Background channels • ttjj • ttbb A.Rozanov TEV4LHC BNL 4 February 2005

  8. ~ qL ~ ~ c02 c01 q h b b b-tagging in SUSY • S-quark - Two b-jets in the final state with h bbq edge 1% error (100 fb-1) ATLAS A.Rozanov TEV4LHC BNL 4 February 2005

  9. p p ~ c01 ~ ~ ~ ~ b c02 g lR b b l l b-tagging for Sbottom/Gluino Mass • require b-tagged jet in addition to dileptons. • sensitivity to sbottom and gluino masses. ~ ~ ~ ~ ~ A.Rozanov TEV4LHC BNL 4 February 2005

  10. b-tagging for SUSY Higgs • Charged Higgs H± with H ± tb or H ± cb or H ± bbW • Charged Higgs tH± with H ± tb • Cascade Neutral Higgs H  h h  b b b b ( trigger …) • Cascade Neutral Higgs H  h h  b b τ τ • Cascade Neutral Higgs H  h h  b b γ γ • Associated Higgs bbA/H with H τ τ • Associated Higgs bbA/H with H bb ( trigger …) • Cascade Neutral Higgs A  Z h with Zμ μ and h b b • Associated Higgs Wh with h bb • Associated Higgs tth with h bb SUSY – b-tagging Eldorado A.Rozanov TEV4LHC BNL 4 February 2005

  11. Performance vertex b-tagging Final state ttH+ttjj -> ttl4j2b (6 jets) ATLFAST jets, 3 layers pixel detector, no pileup, R(jet-jet)=0.7 b=50% Ru=320 b=60% Ru=160 + no b-quark in a cone R=0.6 around light quark jet b=50% Ru=2500 b=60% Ru=680 b-tagging performance is limited by physics: gluon splitting and occasional coincidence between light jet and b-quark directions. A.Rozanov TEV4LHC BNL 4 February 2005

  12. Dependence on η and pT SVX mass εb=60 %, perfect detector, 3D-method, Isolated light jets in ttH,tt A.Rozanov TEV4LHC BNL 4 February 2005

  13. c-rejection dependence on η and pT 3D-method A.Rozanov TEV4LHC BNL 4 February 2005

  14. Prospective of b-tagging • leptons in jets • K0 and Λ0 impact parameters • track quality classification • multiple secondary vertices • η and pT dependences of pdf • hope to reach εb=70 % with Ru=100 A.Rozanov TEV4LHC BNL 4 February 2005

  15. Soft electron b-tagging Electrons • b-jet tagging based on B->D->eX • choose the track with biggest electron-id weight inside the jet • declare as b-jets if the weight is above the threshold • Efficiency for b-jets with electrons (~10 % branching ratio) of pT > 2 GeV/c Pions A.Rozanov TEV4LHC BNL 4 February 2005

  16. Rejection with electron b-tagging Rejection of u-jets R(u) Rejection of jets for 60% of algorithm efficiency working point Ru = 98 ± 8 Rc = 29 ± 2 With conversion package: Ru = 110 ± 8 Rc = 29 ± 2 working point Rejection of c-jets R(c) b-jets id efficiency(alg) A.Rozanov TEV4LHC BNL 4 February 2005

  17. Commissioning Detector Scenario • Initial ATLAS in DC1 layout (2 barrel pixels, 2 pixel disks, no TRT C-wheels) • default inefficiency from the start-up 3% pixels, 2% chips, 1% modules • b-layer inefficiency 1% chips, 0.5% modules • but systematic error big, 2/4 % inefficiencies to be considered • Pixel-SCT alignment after 3 months σRφ=20 μm , σz=60 μm • Pixel-SCT alignment after 6 months σRφ=10 μm , σz=30 μm • Pixel-SCT alignment after 9 months σRφ= 5 μm , σz=15 μm • Direct simulations needed to prove the feasibility of this scenario A.Rozanov TEV4LHC BNL 4 February 2005

  18. Influence of inefficiencies with WH WH events, no pile-up, 2 pixel layers, 3D method • WH μν bb - effect • H  uu - used as “background” mH = 400 GeV mH = 120 GeV A.Rozanov TEV4LHC BNL 4 February 2005

  19. Influence of alignment with ttH • ttH+tt events, mH=120 GeV • Low luminosity pile-up L=2 10 33 cm2 s-1 • Initial layout, 400 μm b-layer z-pitch • 3D b-tagging method • Inefficiency module/chips b-layer 0.5%/1.0%, others 1%/2% • Specification of pixel alignment σRφ=5 μm σz=10 μm • Specification of silicon strips tracker alignment σRφ=12 μm σz=50 μm A.Rozanov TEV4LHC BNL 4 February 2005

  20. Influence of alignment with ttH(120)/ttjj A.Rozanov TEV4LHC BNL 4 February 2005

  21. Pixels ATLAS Destaged pixel layer • Pixels 50 µm x 400 µm • R=5 cm , 9 cm and 12 cm A.Rozanov TEV4LHC BNL 4 February 2005

  22. ATLAS without one pixel layer Ru • default inefficiency 3 % pixels, 2 % chips, 1 % modules • b-layer 1 % chips, 0.5% modules • 400 μm b-layer z-pitch • Reconstructed primary vertex • low luminosity pile-up • DC1 datasets: • WH(120,400)-> bb,uu • ttH-> bb - signal • ttjj -> b l ν b jjjj -background WH(400)-> bb,uu εb A.Rozanov TEV4LHC BNL 4 February 2005

  23. Two versus three pixel layers summary Light jet rejection Rudsg for 60% b-jet tagging efficiency A.Rozanov TEV4LHC BNL 4 February 2005

  24. Two versus three pixel layers summary Light jet rejection Rudsg for 60% b-jet tagging efficiency, ΔRjj > 0.8 , ΔRjbquark > 0.8 , calibration for Initial layout A.Rozanov TEV4LHC BNL 4 February 2005

  25. Conclusions • b-tagging is essential to reach new physics at LHC • Excellent b-tagging performance in ideal LHC detectors • “Devil” is in the performance of the real detector • Realistic studies show acceptable performance Ru~150 at εb=60 % • Low luminosity pile-up degrade by 2-5% • High luminosity pile-up give 10-20% degradation if lepton can not be used for selection of primary vertex A.Rozanov TEV4LHC BNL 4 February 2005

  26. Conclusions • Loss of (15 ± 15)% due to inefficiencies • Loss of 30 % b-tagging for 20 μm alignment • Almost final b-tagging for 5 μm alignment • Extra pixel layer give the gain of ~1.5 in b-tagging A.Rozanov TEV4LHC BNL 4 February 2005

  27. Additional material A.Rozanov TEV4LHC BNL 4 February 2005

  28. Bad tracks • Bad tracks if one of conditions: • one shared hit in b-layer • one shared hit in pixels • two shared hits in SCT • one ambiguous hit in b-layer “Good” tracks “Bad” tracks u u b b A.Rozanov TEV4LHC BNL 4 February 2005

  29. Influence of bad tracks on ttH/ttjj events ttH/ttjj events, mH=120 GeV, with pile-up, 2 pixel layers Initial layout, b-layer 400 μm, inefficiencies modules/chips 1-2 % , b-layer inef. 0.5-1.0 % b- from ttH, u- from ttjj, ATLFAST jets, reconstructed vertex , SV1 method ΔRjj > 0.8 , ΔRjbquark > 0.8 A.Rozanov TEV4LHC BNL 4 February 2005

  30. Bad tracks • Bad tracks if one of conditions: • one shared hit in b-layer • one shared hit in pixels • two shared hits in SCT • one ambiguous hit in b-layer “Good” tracks “Bad” tracks u u b b A.Rozanov TEV4LHC BNL 4 February 2005

  31. Influence of bad tracks on ttH/ttjj events ttH/ttjj events, mH=120 GeV, with pile-up, 2 pixel layers Initial layout, b-layer 400 μm, inefficiencies modules/chips 1-2 % , b-layer inef. 0.5-1.0 % b- from ttH, u- from ttjj, ATLFAST jets, reconstructed vertex , SV1 method ΔRjj > 0.8 , ΔRjbquark > 0.8 A.Rozanov TEV4LHC BNL 4 February 2005

  32. Data sample of ttH/ttjj events for C-wheels ttH/ttjj events, mH=120 GeV, with pile-up, 2 pixel layers Initial layout, b-layer 400 μm, inefficiencies modules/chips 1-2 % , b-layer inef. 0.5-1.0 % b- from ttH, u- from ttjj, ATLFAST jets, reconstructed vertex , ΔRjj > 0.8 , ΔRjbquark > 0.8 , eta > 1.8 A.Rozanov TEV4LHC BNL 4 February 2005

  33. 3D-method for c-Wheels and 2nd pixel disk 3D method A.Rozanov TEV4LHC BNL 4 February 2005

  34. Bad tracks • Bad tracks if one of conditions: • one shared hit in b-layer • one shared hit in pixels • two shared hits in SCT • one ambiguous hit in b-layer “Good” tracks “Bad” tracks u u b b A.Rozanov TEV4LHC BNL 4 February 2005

  35. Influence of bad tracks on ttH/ttjj events ttH/ttjj events, mH=120 GeV, with pile-up, 2 pixel layers Initial layout, b-layer 400 μm, inefficiencies modules/chips 1-2 % , b-layer inef. 0.5-1.0 % b- from ttH, u- from ttjj, ATLFAST jets, reconstructed vertex , SV1 method ΔRjj > 0.8 , ΔRjbquark > 0.8 A.Rozanov TEV4LHC BNL 4 February 2005

  36. Data sample of ttH/ttjj events for C-wheels ttH/ttjj events, mH=120 GeV, with pile-up, 2 pixel layers Initial layout, b-layer 400 μm, inefficiencies modules/chips 1-2 % , b-layer inef. 0.5-1.0 % b- from ttH, u- from ttjj, ATLFAST jets, reconstructed vertex , ΔRjj > 0.8 , ΔRjbquark > 0.8 , eta > 1.8 A.Rozanov TEV4LHC BNL 4 February 2005

  37. 3D-method for c-Wheels and 2nd pixel disk 3D method A.Rozanov TEV4LHC BNL 4 February 2005

  38. SV2 method for C-wheels and 2nd pixel disk SV2 method A.Rozanov TEV4LHC BNL 4 February 2005

  39. Influence of inefficiencies with WH (120) WH events, mH=120 GeV, no pile-up, 2 pixel layers, 3D method A.Rozanov TEV4LHC BNL 4 February 2005

  40. Influence of inefficiencies with WH(400) WH events, mH=400 GeV, no pile-up, 2 pixel layers, 3D method A.Rozanov TEV4LHC BNL 4 February 2005

  41. Influence of inefficiencies with ttH(120) ttH +tt events, mH=120 GeV, low lumi pile-up, Initial, 400 μm b-layer, 3D method A.Rozanov TEV4LHC BNL 4 February 2005

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