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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). Current Activity. Signal generator with tt-system threshold enhancement has been implemented. (Ishikawa, Fujii, Sumino) H bb only

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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. Current Activity • Signal generator with tt-system threshold enhancement has been implemented. (Ishikawa, Fujii, Sumino) • Hbb only • BG study is started. (Uozumi) • Calculation of cross section with MadGraph • Generation of background

  3. BG Study • Uozumi-san reviewed four papers on ttH analysis • ttg will be a dominant BG, but ttZ, tt and WW will also be non-negligible BGs. • Other BGs (WWH, ZZH, …) may be negligible • He calculated cross sections of BG modes with MadGraph for Ecm=500GeV and mH=120GeV. • e+e-g ttg … 33.7 fb • e+e-g ttg g ttbb … 0.67 fb • e+e-g ttZ … 1.07 fb • e+e-g WWH … 5.69 fb • e+e-g ZZH … 0.56 fb • e+e-g ttWW, ttZZ … too small to calculate

  4. Signal Generator • The generator we used is only for Hbb decays • Ishikawa and Fujii-san modified the generator • Higgs never decay in current generator. • The output is passed to Pythia and Higgs decays anything allowed by the SM. e+e- ttH unpolarized

  5. Event Display • Very dense for 8 jet event. • Challenging for reconstruction. Ecm=500GeV MH=120GeV ttH(bW)(bW)(bb)(bcs)(bcs)(bb) ttH(bW)(bW)(bb)(bud)(ben)(bb) 6 jet 8 jet

  6. Beam Polarization • Electron and positron polarizations are one of the key issues for LC physics since they increase the signal s or suppress BG s. • There are two effects • spin 1 combinations • Coupling to SU(2)L gauge boson • EM interaction respects Parity but weak interaction does not. • Coupling to Z boson is • For electron positron case, the coupling is not so different for left handed or right handed polarization since the Weiburg angle is close to quarter. But top case, left handed electron gives larger cross section. e- e+ e- e+ 0.5 =0.25gR2 0.5 0.5 0.5 =0.25gL2 1.0 =1.0gL2 1.0 P=(Pe- ,Pe+)=(0,0) P=(-1,+1)

  7. Beam Polarization for ttH • I have calculated the cross section as a function of Ecm for P=(-1.0, 0.0), P=(1.0, 0.0) and P=(-0.8, 0.6) with M_H = 120 GeV and M_t = 170.9GeV • s = 1.2fb for P=(-0.8, 0.6) and Ecm=500GeV

  8. Mass dependence • Mass dependence of cross section is also calculated with P=(-0.8, 0.6). • Mh>170GeV seems to be difficult at ILC 1st stage (Ecm~500GeV)

  9. Summary and Plan • Dominant BGs are ttg, ttZ, tt and WW. • Cross sections of BG modes are calculated. • Now Higgs can decay to anything allowed by the SM. • Electron and Positron Polarizations are very useful to enhance signal cross section. • s = 1.2fb for Ecm=500GeV, P=(-0.8, 0.6) and Mh=120GeV • Mh>170GeV seems to be difficult at ILC 1st stage. • Calculate BG cross sections other than Ecm=500GeV • Generate signal and backgrounds • Start analysis

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