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Status of ttH Group Activity

Status of ttH Group Activity. Akimasa Ishikawa (Saga University) Satoru Uozumi (Shinshu University) Keisuke Fujii (KEK) Yukinari Sumino (Tohoku University). Introduction. Top Yukawa coupling is a fundamental parameter in the SM.

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Status of ttH Group Activity

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  1. Status of ttH Group Activity Akimasa Ishikawa (Saga University) Satoru Uozumi (Shinshu University) Keisuke Fujii (KEK) Yukinari Sumino (Tohoku University)

  2. Introduction • Top Yukawa coupling is a fundamental parameter in the SM. • Recent study shows that LHC seems to be very difficult to measure Yt. • ILC is the only place to measure it (SLHC also?) • NLO + Threshold effect of tt system + e+ polarization enhance the s(e+e- ttH) by factor 4. • Born s=0.074fb (including ISR and bremstrahlung effects) • Mh=120GeV, Mt1S=180GeV, Ecm=500GeV and (Pe-, Pe+)=(-0.9,0.0) • NLO s=0.18fb • Estimate sensitivity of Yt at the ILC first stage (Ecm~500GeV) • With Higgs mass of 120 ~ 200 GeV hep-ph/0512246 Yt

  3. Signal e+e-  ttH • mH=120 ~ 200 GeV • Ethre = 2*mt+mH = 470 ~ 550 GeV • s(Ethre+ a) = O(0.1) fb  O(100) events with 1000/fb • ~1fb with mH=120GeV at 550GeV • Decay • ttH  bWbW (WW or ZZ)  10 fermions • High jet multiplicity • Background should be different from ZH • We can share the background generator/production with ZHH group?

  4. Possible Background • High jet multiplicity modes • tt(g) • s ~ 500fb @ 500GeV • bWbW(qq) 6(8) fermions • ttZ • s ~ ??? @ • bWbWqq  8 fermions • WWH • s = ??? fb •  WW(WW or ZZ)  8 fermions • Suppressed by b tagging? • ZZH • s = ??? fb •  ZZ (WW or ZZ)  8 fermions • ZH  ttH • Identical to signal (interference) • The amplitude is smaller (ignorable) compared to signal according to Fujii-san. • ttWW, ttZZ • s = ??? fb, should be small • Irreducible background • Low jet multiplicity but large cross section • qq • WW

  5. Analysis Strategy • Exclusive Analysis based on decay mode. • Reconstruct H, W and t from final state fermions. • All jet mode • Lepton mode • Tau mode • Neutrino mode • Cleaner but efficiency should be low • Inclusive analysis based on fermion counting • Count the number of fermions (jet, lepton and neutrino) • Event topology selection (sphericity, FW moment, etc.) • b tagging • Loose mass selection on the W, t or H. • Dirtier against to exclusive, but efficiency is high • Number of signal is low O(100) so inclusive one seems to be better.

  6. Who is working on what? • Ishikawa : signal generator • Uozumi : background cross sections • Fujii : supervising • Sumino : theory side

  7. Signal Generator • Tree level calculation is done by HELAS. • To implement the threshold enhancement, Green’s function G(p;E), described below, is multiplied to the tree level differential cross section. • This technique is used for e+e- ttbar generator written by Fujii-san. • I just implemented the threshold effect.

  8. Generator output • Enhanced by ~2. • Different from hep-ph/0512246, EH and s Mtt EH s=0.17fb Born s=0.18fb s=0.074fb s=0.39fb w/ threshold effect

  9. Summary • NLO + Threshold effect of tt system + e+ polarization enhance the s(e+e- ttH) by factor 4. • s~0.36fb with Mh=120GeV and Ecm=500GeV • Cross section is O(0.1)fb • Inclusively reconstruct signal • Threshold enhancement is implemented • Cross section and EH Shape are different from hep-ph/0512246 • Need to check

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