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Higgs self-coupling at photon collider (AA->HH Study)

Higgs self-coupling at photon collider (AA->HH Study). Shin- ichi Kawada AdSM , Hiroshima University. Outline. almost same contents @ LCWS11. Motivation Signal & Background Simulation & Analysis Result Summary & Next plan. Motivation.

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Higgs self-coupling at photon collider (AA->HH Study)

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  1. Higgs self-coupling at photon collider(AA->HH Study) Shin-ichi Kawada AdSM, Hiroshima University 23rd General Meeting @ KEK (2011/11/5)

  2. Outline almost same contents @ LCWS11 23rd General Meeting @ KEK (2011/11/5) Motivation Signal & Background Simulation & Analysis Result Summary & Next plan

  3. Motivation Final goal : measuring Higgs self-coupling constant λ Higgs self-coupling constant in the SM deviation parameter from the SM Before the final goal… We have to investigate the feasibility of measurement of Higgs pair creation in a PLC. 23rd General Meeting @ KEK (2011/11/5)

  4. Optimizing collision energy mH = 120GeV ∫Ldt = 1000fb-1 η = η’ = 1, ηBG = 0 270GeV (GeV)

  5. Beam parameters based on TESLA optimistic parameter x=3.76 in this study

  6. Luminosity distribution simulated with CAIN (GeV)

  7. Signal & Backgrounds γγ->WW γγ->ZZ tt threshold 270GeV

  8. # of events Signal γγ->HH :16 events/year Main backgrounds γγ->WW :1.462*107 events/year γγ->ZZ :1.187*104 events/year γγ->4b :1.37*105 events/year 23rd General Meeting @ KEK (2011/11/5)

  9. Event signature (1) b-jet b-jet mass distribution Mbb (GeV) 23rd General Meeting @ KEK (2011/11/5) • γγ->HH • HH->4b • Mbb = MH (120GeV)

  10. Event signature (2) 23rd General Meeting @ KEK (2011/11/5) • γγ->WW • σγγ->WW ~ 106σγγ->HH • suppressed by b-tagging • γγ->ZZ • ZZ->4b same as HH->4b • discriminate only by mass difference • γγ->4b • Mass distribution is different from signal, but still have events near signal region (~120GeV). • Angular distribution is different from signal.

  11. Simulation & Analysis 23rd General Meeting @ KEK (2011/11/5) • Event generation & Detector simulation • Event reconstruction • jet clustering • b-tagging • nsig method • jet pairing • Event selection • pre-selection • Neural Network (NN)

  12. Event reconstruction (1) information of mass M1, M2 : reconstructed mass i : H, W, Z, bb σ2j : mass resolution ex: χH2 distribution χH2 23rd General Meeting @ KEK (2011/11/5)

  13. Event reconstruction (2) :b-tagging nsig method When there are noffv tracks which satisfy this equation, we regarded this quark as a b-quark. relatively simple b-tagging method can be improved by further study 23rd General Meeting @ KEK (2011/11/5)

  14. Event selection by Neural Network (NN) N : # of events 23rd General Meeting @ KEK (2011/11/5) • 3 steps • W filter • 4b filter • Z filter • Maximize statistical significance

  15. Distribution of NN inputs:WW HH WW HH WW # of b-flavor jet with (nsig = 3.5, noffv = 2) analysis χH2 23rd General Meeting @ KEK (2011/11/5)

  16. Distribution of NN inputs:4b HH 4b HH 4b maximum |cosθ of jet| # of tracks 23rd General Meeting @ KEK (2011/11/5)

  17. Distribution of NN inputs:ZZ HH ZZ HH ZZ χZ2 χH2 23rd General Meeting @ KEK (2011/11/5)

  18. Cut summary (training sample) = (test sample)

  19. Cut summary (training sample) ≠ (test sample)

  20. Further improvement correct color singlet information improve mass resolution, b-tagging efficiency We investigated using generator information for HH, WW, ZZ (not for 4b). 23rd General Meeting @ KEK (2011/11/5) WW BG : almost completely suppressed! 4b & ZZ BG remained Possible improvement --- jet clustering

  21. Improve mass resolution JADE clustering Ex: mass distribution of HH & ZZ BG HH ZZ perfect jet clustering HH ZZ 23rd General Meeting @ KEK (2011/11/5)

  22. Cut summary with perfect jet clustering(training sample) = (test sample)

  23. Cut summary with perfect jet clustering(training sample) ≠ (test sample)

  24. Summary 23rd General Meeting @ KEK (2011/11/5) • We investigated γγ->HH in a gamma-gamma collider based on TESLA optimistic parameters. • Possible to suppress huge backgrounds with improved jet clustering. • Significance ~ 5 with 5 year PLC run • Next plan • Writing a paper -> now updating Ver.0 -> Ver.1

  25. Backup slides 23rd General Meeting @ KEK (2011/11/5)

  26. About PLC Electrons backward Compton scattering gamma-gamma collision 23rd General Meeting @ KEK (2011/11/5)

  27. Comparison of γγ and e+e- process : Higgs self-coupling Contribution of self-coupling is different way. Energy threshold of γγ process is lower than e+e- process. 23rd General Meeting @ KEK (2011/11/5)

  28. γγ->bbbb (4b) events b γ γ b b b : color string b b γ γ b b (2-jet invariant mass) < 15GeV were cut. We assume that we can cut these events. --> 5.872*104 events/year 23rd General Meeting @ KEK (2011/11/5)

  29. Calculation of 4b BG d -> b ELWK = 2 QCD = 2 Calculated with GRACE

  30. Jet clustering JADE clustering pi : 4-momentum of particle i Evis : visible energy Ycut : Ycut value of jet clustering 23rd General Meeting @ KEK (2011/11/5)

  31. Event selection --- pre-selection pre-selection β>0.05, |cosθ|<0.99 more than 3 b-flavor jets with (nsig = 3.0, noffv = 1) analysis more than 2 b-flavor jets with (nsig = 3.0, noffv = 2) analysis β : Lorentz factor of reconstructed particle θ : angle between reconstructed particle and beam axis b-tagging to suppress huge WW BG mainly 23rd General Meeting @ KEK (2011/11/5)

  32. Sphericity, Y-value normalized momentum tensor Mab pi : momentum of particle i 3*3 matrix eigenvalue 23rd General Meeting @ KEK (2011/11/5)

  33. W filter 23rd General Meeting @ KEK (2011/11/5) • 9 input parameters • χH2,χZ2 • visible energy • # of tracks • Ycut value of jet clustering • longitudinal momentum, transverse momentum • # of b-flavor jets (nsig = 3.5, noffv = 1 analysis) • # of b-flavor jets (nsig = 3.5, noffv = 2 analysis)

  34. 4b filter 10 : invariant mass of bb system 23rd General Meeting @ KEK (2011/11/5) • 17 input parameters • no relation to χ2 (11) • visible energy, # of tracks, Ycut value of jet clustering, thrust, sphericity, Y-value, cosθ of jet (4), maximum |cosθ of jet| • jet pairing of least χH2(3) • χH2, cosθ of 2-jet (2) • jet pairing of least χbb2 (3) • χbb2, cosθ of 2-jet (2)

  35. Z filter 23rd General Meeting @ KEK (2011/11/5) • 10 input parameters • χH2, χW2, χZ2 • energy of 2-jet (2) • visible energy • # of tracks • longitudinal momentum • # of b-flavor jets (nsig = 3.5, noffv = 1 analysis) • # of b-flavor jets (nsig = 3.5, noffv = 2 analysis)

  36. Cut summary(training sample) = (test sample)JADE clustering & 4b (optimistic) 23rd General Meeting @ KEK (2011/11/5)

  37. Cut summary(training sample) = (test sample)JADE clustering & 4b (pessimistic) 23rd General Meeting @ KEK (2011/11/5)

  38. Cut summary (training sample) = (test sample)perfect jet clustering & 4b (optimistic) 23rd General Meeting @ KEK (2011/11/5)

  39. Cut summary (training sample) = (test sample)perfect jet clustering & 4b (pessimistic) 23rd General Meeting @ KEK (2011/11/5)

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