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Higgs pair production at photon collider

Higgs pair production at photon collider. ILC Physics WG general meeting 21. November 2009 Hiroshima University Nozomi Maeda. Introduction. Photon Linear Collider (PLC) is gamma-gamma collision option in ILC.

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Higgs pair production at photon collider

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  1. Higgs pair production at photon collider ILC Physics WG general meeting 21.November 2009 HiroshimaUniversity Nozomi Maeda

  2. Introduction Photon Linear Collider (PLC) is gamma-gamma collision option in ILC. We study feasibility of measurement of Higgs self-coupling constant l=lSM(1+dk) by gg->HH This process occurs at low energy(than e+e-). l contribution to cross section is different.

  3. Energy optimization dk=+1 L:Luminosity(assume 1000fb-1) h:detection efficiency s:cross section hB:background suppression dk=-1 Higgs mass=120GeV

  4. (+,+), (-,-) Background large background :　　 　gg->WW (sB～90pb)　 　　cf.) Signal:s = 0.044fb 0.044fb/90pb = 4.9×10-7 10-7background suppression is necessary.

  5. Luminosity spectrum Simulation by CAIN. total luminosity of photon collision = 1.26×1035cm-2s-1 effective Xsec(Signal) = 0.013fb → 16event/year effective Xsec(BG) = 11,600fb → 1.467×107event/year hB<10-6 is required.

  6. Analysis • gg->HH 　H -> bb or WW* or gg … Signal:HH->4b Background:WW->4quark H->bb mode has the largest Branching Ratio (when Higgs mass = 120GeV, B.R.=67.8%). reconstruct particles from jet pairs that has the smallest c2. M1,M2 = reconstructed particle mass M = MH or MW　 s2j = 2jets mass resolution

  7. gg->WW rejuction • use Neural Net(JetNet) to separate gg->HH from gg->WW. • # of generated events : Signal = 5.00×104 BG = 7.50×107 • # of nodes : input = 9, hidden = 18, output = 1 • pre-Selection : # of loose b-tagged jets > 2 & # of tight b-tagged jets > 1 (loose : nsig=3.0, noffv=1 tight : nsig=3.0, noffv=2)

  8. NN output • input parameters : c2H, c2W, # of tracks, momentum(transverse, longtidunal), Visible Energy, ycut, # of b-tagged jets(loose, tight) (loose : nsig=3.5, noffv=1 tight : nsig=3.5, noffv=2) black:BG blue:Signal NNout > 0.98 If PLC runs for 5years...Signal : 16×5×hSig ≒ 12.5 Background : 1.467×107×5×hBG ≒ 3.9 significance = 3.1s

  9. gg->ZZ background gg->ZZ Xsec ≒ 50fb@300GeV photon helicity = (+1, +1) Integrate over 8deg<q<172deg (generated by Gounaris’s gamgamZZ code: hep-ph/0610085. offered by Tsumura-san.)

  10. gg->ZZ background x=3.76 gg->ZZ effective Xsec　　　 ≒ 9.6fb→1.2×104events/year Integrate over 8deg<q<172deg (generated by Gounaris’s gamgamZZ code: hep-ph/0610085. offered by Tsumura-san.)

  11. f Z g f f g Z f gamgamZZ code HELAS gg->ZZ->4fevent generator ZZ decay modes are ... q = light quark bbqq (12.9%), ccqq (10.3%), qqqq (18.3%), bbbb (2.28%), bbcc (3.62%), cccc (1.44%) bbbb……be background source． → simulate gg->ZZ event, and study how to reject gg->ZZ. → develop gg->ZZ->4fevent generator use gamgamZZ code and HELAS for calculating helicity amplitude.

  12. g Z Z g (not includes Z decay mode and Luminosity) gg->ZZ event generator Xsec distribution total Xsec = 49.8fb (consistent with gamgamZZ code)

  13. Summary • We study feasibility of measurement of Higgs self-coupling constant at PLC. • gg->WW background is 106 times larger than gg->HH signal. • Neural Net with b-tagging and kinematics can reject almost all gg->WW background. • gg->ZZ event generator developing in progress. • Next plan is including Z decay mode and Luminosity spectrum to gg->ZZ event generator.

  14. gg->4b background b-tagging cannot reject gg->4b too. Xsec(not convolute gg luminosity) = 2.81fb@optimum gg energy + and other diagrams

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