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Higgs pair production at photon collider

This study explores the feasibility of measuring the Higgs self-coupling constant using the Photon Linear Collider (PLC) at Hiroshima University. Specifically, we focus on the rare process gg → HH to assess the effectiveness of energy optimization and background suppression techniques, given a Higgs mass of 120 GeV. Through simulation frameworks and event reconstruction methods, we estimate a signal event rate of approximately 16 events per year, enabling observation with a significance of 2.96σ over five years, while highlighting the importance of b-tagging in separating signal from background events.

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Higgs pair production at photon collider

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  1. Higgs pair production at photon collider HiroshimaUniversity Nozomi Maeda 13.July 2009

  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 l?

  4. Energy optimization dk=+1 L:Luminosityh:detection efficiency s:cross section hB:background suppression dk=-1 Higgs mass=120GeV

  5. Background (+,+), (-,-) main background is　　　gg->WW (sB～90pb)　　　cf.) Signal:s = 0.044fb 0.044fb/90pb = 4.9×10-7 10-7background suppression is necessary. gg->tT does not occur. Optimum energy is below tT threshold.

  6. Simulation Framework CAIN (Luminosity) Signal : gg->HH BG : gg->WW theoretical calc. program (helicity amplitude) Helas (helicity amplitude) BASES/SPRING (Integration, Generation) Quick Detector Simulator pythia (parton shower，hadronization) Analysis

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

  8. Signal ： gg->HH 　H -> bB or WW* or gg … • Background : gg->WW 　　W -> ud or cs or en… Analysis choose HH->4b(Branching ratio = 0.43). background:WW->4quark →reconstruct particles, and try to distinguish them.

  9. 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

  10. mass distribution black:HH->Allred:WW->All c2 distribution s(gg->HH)×105 choose this region Selection by c2 isnot enough to suppress background. →b-tagging is necessary.

  11. b-tagging by simulation b-tag requirement : nsig = 3.5, noffv = 2 # of b-tagged jets = 4 cutting line

  12. Event selection Background : 45,000,000event -> 0event Signal : 50,000event -> 5,483event (hSignal=0.110) If PLC runs for 5 years... 16events/year×5years×0.110 ≒ 9events → 2.96s

  13. Summary • We study feasibility of measurement of Higgs self-coupling constant l at PLC. • If Higgs mass = 120GeV, optimized photon collision energy is 270GeV. • # of Signal event is expected 16events/year with PLC parameter(TESLA optimistic). • Selection by b-tagging and kinematics parameters can suppress almost gg->WW. • gg->HH can be observed with 2.96s in 5years.

  14. Next plan • consider HH->bBWW*(B.R.=0.18). • consider gg->4b • use FlavourGetter in order to study remaining events.

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