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Feasibility study of Higgs pair production in a Photon Collider

Feasibility study of Higgs pair production in a Photon Collider. Tohru Takahashi Hiroshima University for S.Kawada , N.Maeda , K.Ikematsu , K.Fujii,Y.Kurihara ,,,. IWLC2010 CERN. Higgs Physics w/ PLCs. Two photon decay width of light higgs 2% ~ 8% for Mh = 129geV ~ 160GeV

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Feasibility study of Higgs pair production in a Photon Collider

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  1. Feasibility study of Higgs pair production in a Photon Collider Tohru Takahashi Hiroshima University for S.Kawada, N.Maeda, K.Ikematsu, K.Fujii,Y.Kurihara ,,, IWLC2010 CERN 17th General Meeting @ KEK

  2. Higgs Physics w/ PLCs • Two photon decay width of light higgs • 2% ~ 8% for Mh = 129geV ~ 160GeV • Discovery potential of heavy Mh (LHC wedge) • ~< 360GeV • CP w/ Linear polarization • ~10% precision for 120GeV Feasibilities for standard Higgs processes have been understood rare processes scenario for PLC run before e+e- T.Takahashi Hiroshima

  3. Self-coupling constant in the SM Parameter of deviation from the SM Purpose of this study Final goal: Study of Higgs self-coupling See feasibility of the measurement of Higgs pair creation in PLC. how may events expected? possible to suppress background? 17th General Meeting @ KEK

  4. Sensitivity vs energy η=η’=1,ηB=0 T.Takahashi Hiroshima

  5. Beam parameters (based on TESLA optimistic) T.Takahashi Hiroshima

  6. Luminosity Distribution x=3.76 ~16events/year 13events@Ltot=1000fb-1

  7. gg->WW->4q • (1.462*107events/year) • gg->ZZ->4b • (1.187*104events/year) Signal & Main backgrounds Signal：gg->HH->4b (16.4events/year) gg->WW Main backgrounds gg->ZZ t tbar threshold 270GeV

  8. Simulation & Analysis • Event generation and detector simulation • Reconstruct events • Jet clustering (reconstruct jets) • b-tagging (identification of b-quark) • nsig method was used in this study. • Reconstruct particles (determination of jet combination) • Selection • Selection with Neural Network (NN)

  9. Reconstruct particles We have to choose two jets from 4 jets (j1-j4) in order to reconstruct original particle. ->There are 3 patterns of combination in a event. ->The jet of the least χ2 was chosen to be the most probable combination. M1, M2：reconstructed particle mass MH：Higgs mass σ2j：mass resolution

  10. Selection (1) β：Lorentz factor of reconstructed particle θ：Angle between reconstructed particle and initial photon beam 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 b-tagging

  11. Selection (2) --- Neural Network (NN) • 9 input parameters： • χH2 ,χZ2, • transverse (longitudinal) momentum, • # of b-flavor jets (2 patterns), • visible energy, • Ycutvalue of jet clustering, • # of tracks • Maximize statistical significance N: # of events occurring in 5 years η: selection efficiency Sig: signal BG: background

  12. Distribution of input parameters (1) HHWWZZ

  13. HH + WW BG HH WW Results of NN analysis --- WW BG almost suppress WW background. NN output

  14. HH + ZZ BG HH ZZ Results of NN analysis --- ZZ BG not bad but not enough NN output

  15. attempt for improvement • previous analysis apply NN selection for WW and ZZ background separately. • possible improvement by jet clustering if both WW and ZZ cut are applied

  16. HH + ZZ BG HH ZZ Analysis with CheatJetFinder --- ZZ BG CheatedJetFinder: 100% correct parton assignment using generator information suppress ZZ background w/ improved cluctering NN output

  17. HH + WW BG HH WW Analysis with CheatJetFinder --- WW BG good background suppresion for WW too NN output

  18. Summary • We tried to see gg -> HH in a photon collider based on TESLA optimistic parameters. • gg CM energy of 270GeV is optimum for mh =120GeV • backdournds • gg->WW has 106 times lager cross section • gg->ZZ has 103times lager cross section • It seems possible to suppress backgrounds with improved jet clustering technique. • statistical significance of 4.6 expected for WW and ZZ cut with perfect jet clustering • more to do • optimize NN training • study jet clustering improvement (it is not just for HH analysis • gg->bbbbbackgroud • we believe it is small for dangerous kinematical region • higher Higgs mass

  19. Backup slide

  20. Optimization of CM energy L：luminosity (1000fb-1) σ：cross-section SM：standard model δκ：deviation from the standard model In order to simplify the discussion, we set the detection efficiency to be 100% and there are no background. Collision energy of gamma-gamma ~270GeV We set the optimized CM energy is equal to 270GeV.

  21. Luminosity distribution We adjusted the parameters of the laser and e- beam to have a peak at the optimum energy. Effective cross-section of Higgs pair creation was calculated 0.013fb. 16.4events/year(1year = 107sec) 17th General Meeting @ KEK

  22. Effective cross-section • AA->HH: 0.013fb • AA->WW: 11.6pb • AA->ZZ: 9.42fb 17th General Meeting @ KEK

  23. Policy of analysis The highest decay branching ratio is HH->4b mode (45.9%) WW->4b mode: 0% ZZ->4b mode: 2.3% We tried to reconstruct events which generated 4b. 17th General Meeting @ KEK

  24. pi: 4-momentum of particle Evis: Visible energy Ycut: Any value Jet clustering We can obtained the information of 4-momentum of original quark if we can obtain the information of original jets, so we have to reconstruct original jets first. JADE clustering When particle i and j satisfy this equation, we calculate 4-momentum of sum of these particles. ->reconstruct jets Since HH->4b reaction is 4-jets mode, we applied forced 4-jets analysis. 17th General Meeting @ KEK

  25. nsig method L: The least approach to the interaction point of the track in the plane perpendicular to the beam σL: Distance resolution of detector nsig、noffv： Any value b-tagging Method of identify b-quark. When there are noffv tracks which satisfy this equation, we regarded this quark as b-quark. ->identification of b-quark 17th General Meeting @ KEK

  26. Accuracy of b-tagging Efficiency for AA->HH->4b events Contamination for AA->WW events 17th General Meeting @ KEK

  27. Distribution of input parameters (2) HHWWZZ # of b-flavor jets with (nsig=3.5, noffv=1) analysis # of b-flavor jets with (nsig=3.5, noffv=2) analysis 17th General Meeting @ KEK

  28. Distribution of input parameters (3) HHWWZZ longitudinal momentum transverse momentum 17th General Meeting @ KEK

  29. Distribution of input parameters (4) HHWWZZ # of tracks visible energy Ycut value of jet clustering 17th General Meeting @ KEK

  30. Verification of statistical error of NN training Kawada ON Kawada OFF1 Kawada OFF2 weights Maeda events 13089 2729 13263 2916 13276 2941 13788 3041 Maeda 1.55 1.52 1.52 1.55 29935 86944 Kawada-ON 13047 2832 14254 3488 13880 3293 13738 3144 29958 87484 1.52 1.50 1.51 1.52 Kawada-OFF1 13047 2735 13168 2896 13575 3057 13738 3057 1.54 1.52 1.52 1.54 29958 87057 Kawada-OFF2 13391 2904 12830 2723 12538 2575 13291 2846 29823 87142 1.54 1.52 1.53 1.54 # of remained HH,# of remained ZZ,Maximum significance 17th General Meeting @ KEK

  31. : Higgs self-coupling Features of Higgs pair creation in PLC Gamma Gamma process cf: e+ e- process Final state: 2 particles Final state: 3 particles Comparing with e+e- collision Self coupling contribute different way Lower energy threshold 17th General Meeting @ KEK

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