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Higgs pair production at photon collider

Higgs pair production at photon collider. ILC Physics WG general meeting 19. September 2009 Hiroshima University Nozomi Maeda. PLC in ILC. 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 19.September 2009 HiroshimaUniversity Nozomi Maeda

  2. PLC in ILC Photon Linear Collider (PLC) is gamma-gamma collision option in ILC. Measurement of basic physical quantity of Higgs at PLC has been studied. e.g.)the two photon decay width of Higgs. We study feasibility of mesurement of rare process at PLC.

  3. gg->HH Measurement of Higgs self-coupling constant l=lSM(1+dk) by gg->HH final state is 2particles　include loop diagram 1. This process occurs at low energy(than e+e-). 2. l contribution to cross section is different. →Can PLC measure Higgs self-coupling constant ?

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

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

  6. 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.

  7. Analysis • gg->HH 　H -> bb or WW* or gg … H->bb mode has the largest Branching Ratio (when Higgs mass = 120GeV, B.R.=67.8%). Signal:HH->4b Background:WW->4quark

  8. Event reconstruction choose 2jets from 4jets, and reconstruct Higgs(or W-boson) from this 2jets. → 3 combinations for 1event. → choose a combination that has the smallest c2. M1,M2 = reconstructed particle mass M = MH or MW　 s2j = 2jets mass resolution

  9. use Neural Net • use Neural Net(JetNet) to optimize selection criteria. • # 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)

  10. 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

  11. 25 20 15 10 5 0.25 0.30 0.35 0.40 0.45 0.50 gg->ZZ background gg->ZZ effective Xsec　　　 ≒ 6fb → 7.6×103events/year Integrate over 30deg<q<150deg (generated by Gounaris’s gamgamZZ code: hep-ph/0610085. offered by Tsumura-san.)

  12. estimate gg->ZZ event ZZ decay mode 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.

  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. • Next plans are Simulation gg->ZZ events and studying how to reject gg->ZZ.

  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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