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Feasibility study of measurement of Higgs pair creation in a gamma-gamma collider

Feasibility study of measurement of Higgs pair creation in a gamma-gamma collider. Shin- ichi Kawada Advanced Sciences of Matter, Hiroshima University. Collaborators : Katsumasa Ikematsu (Univ. Siegen), Tohru Takahashi (Hiroshima Univ.),

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Feasibility study of measurement of Higgs pair creation in a gamma-gamma collider

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  1. Feasibility study of measurement of Higgs pair creation in a gamma-gamma collider Shin-ichi Kawada Advanced Sciences of Matter, Hiroshima University Collaborators : KatsumasaIkematsu (Univ. Siegen), Tohru Takahashi (Hiroshima Univ.), Keisuke Fujii (KEK), YoshimasaKurihara (KEK), and ILC physics working group LCWS11 @ Granada, Spain (2011/9/29)

  2. Outline LCWS11 @ Granada, Spain (2011/9/29) Motivation Signal & Background Simulation & Analysis Result Summary

  3. T. Takahashi’s talk @ IWLC2010 My talk is including these topics. LCWS11 @ Granada, Spain (2011/9/29)

  4. 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. LCWS11 @ Granada, Spain (2011/9/29)

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

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

  7. Luminosity distribution simulated with CAIN (GeV)

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

  9. # 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 LCWS11 @ Granada, Spain (2011/9/29)

  10. Event signature (1) b-jet b-jet mass distribution Mbb (GeV) LCWS11 @ Granada, Spain (2011/9/29) • γγ->HH • HH->4b • Mbb = MH(120GeV)

  11. Event signature (2) LCWS11 @ Granada, Spain (2011/9/29) • 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.

  12. Simulation & Analysis LCWS11 @ Granada, Spain (2011/9/29) • Event generation & Detector simulation • Event reconstruction • jet clustering • b-tagging • nsig method • jet pairing • Event selection • pre-selection • Neural Network (NN)

  13. Event reconstruction (1) information of mass M1, M2 : reconstructed mass i : H, W, Z, bb σ2j : mass resolution ex: χH2 distribution χH2 LCWS11 @ Granada, Spain (2011/9/29)

  14. 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 LCWS11 @ Granada, Spain (2011/9/29)

  15. Event selection by Neural Network (NN) N : # of events LCWS11 @ Granada, Spain (2011/9/29) • 3 steps • W filter • 4b filter • Z filter • Maximize statistical significance

  16. Distribution of NN inputs --- WW HH WW HH WW # of b-flavor jet with (nsig = 3.5, noffv = 2) analysis χH2 LCWS11 @ Granada, Spain (2011/9/29)

  17. Distribution of NN inputs --- 4b HH 4b HH 4b maximum |cosθ of jet| # of tracks LCWS11 @ Granada, Spain (2011/9/29)

  18. Distribution of NN inputs --- ZZ HH ZZ HH ZZ χZ2 χH2 LCWS11 @ Granada, Spain (2011/9/29)

  19. Cut summary

  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). LCWS11 @ Granada, Spain (2011/9/29) 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 LCWS11 @ Granada, Spain (2011/9/29)

  22. Cut summary with perfect jet clustering

  23. Summary T. Suehara’s talk, T. Tanabe’s talk in this workshop LCWS11 @ Granada, Spain (2011/9/29) • 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 • Further study • jet clustering • b-tagging • other decay modes

  24. Backup slides LCWS11 @ Granada, Spain (2011/9/29)

  25. About PLC Electrons backward Compton scattering gamma-gamma collision LCWS11 @ Granada, Spain (2011/9/29)

  26. 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. LCWS11 @ Granada, Spain (2011/9/29)

  27. γγ->b b-bar b b-bar (4b) events b γ γ b b-bar b-bar : color string b b γ γ b-bar b-bar (2-jet invariant mass) < 15GeV were cut. We assume that we can cut these events. --> 5.872*104 events/year LCWS11 @ Granada, Spain (2011/9/29)

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

  29. Jet clustering JADE clustering pi : 4-momentum of particle i Evis : visible energy Ycut : Ycut value of jet clustering LCWS11 @ Granada, Spain (2011/9/29)

  30. 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 LCWS11 @ Granada, Spain (2011/9/29)

  31. Sphericity, Y-value normalized momentum tensor Mab pi : momentum of particle i 3*3 matrix eigenvalue LCWS11 @ Granada, Spain (2011/9/29)

  32. W filter LCWS11 @ Granada, Spain (2011/9/29) • 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)

  33. 4b filter 10 : invariant mass of b b-bar system LCWS11 @ Granada, Spain (2011/9/29) • 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 χγ2(3) • χγ2, cosθ of 2-jet (2)

  34. Z filter LCWS11 @ Granada, Spain (2011/9/29) • 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)

  35. Cut summaryJADE clustering & 4b (optimistic) LCWS11 @ Granada, Spain (2011/9/29)

  36. Cut summaryJADE clustering & 4b (pessimistic) LCWS11 @ Granada, Spain (2011/9/29)

  37. Cut summaryperfect jet clustering & 4b (optimistic) LCWS11 @ Granada, Spain (2011/9/29)

  38. Cut summaryperfect jet clustering & 4b (pessimistic) LCWS11 @ Granada, Spain (2011/9/29)

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