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e + e - g ttH Past Experimental (simulation) Studies and BG cross-section by MadGraph

e + e - g ttH Past Experimental (simulation) Studies and BG cross-section by MadGraph. Sep-27 2007 physics WG meeting S. Uozumi (Shinshu). Past Study - 1. ttg. A study concentrates on cms=500 GeV, Higgs mass 100 ~ 140 GeV, ttH g bbbbWW g bbbb l n qq channel.

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e + e - g ttH Past Experimental (simulation) Studies and BG cross-section by MadGraph

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  1. e+e-gttHPast Experimental (simulation) Studiesand BG cross-section by MadGraph Sep-27 2007 physics WG meeting S. Uozumi (Shinshu)

  2. Past Study - 1 ttg • A study concentrates on cms=500 GeV, • Higgs mass 100 ~ 140 GeV, • ttH g bbbbWW g bbbb l n qq channel. • Assume perfect b-tag, no detector simulation. • HERAS (diagram), VEGAS and RAMBO (integration) are used. • First evaluation of non-negligible • QCD background (ttg). • Also mention the ttZ is not small either. • Also mention that some BG processes • (e+e-gW+*W , W+* g Htb g HbbW • or e+e- g t*b, t* g tH). • may contains top Yukawa coupling. ttg g 4blnqq S. Moretti, Phys. Lett. B 452 (1999) 338 ttZ ttZ g 4blnqq ttHg 4blnqq (solid) ttH (dash) All bbWWg g 4blnqq ttg g 4blnqq All ZbbWW g 4blnqq ttZ g 4blnqq ttHg 4blnqq (solid) Table of cross-sections (MH = 130 GeV, no cuts) All bbWW and ttH g 4blnqq (dash) Higgs Mass (GeV)

  3. Past Study - 1 S. Moretti also demonstrates bb di-jet mass and jet energy are useful to reject the QCD and ttZ backgrounds. M23 M12 E1 E3 M24 M13 Solid … ttH Dash … ttZ Dot … ttg b-Jets are ordered by their energy E2 E4 M34 M14 Jet energy Ei (GeV) bb di-met mass Mij (GeV) Especially M34 and E4 have the discrimination power for the signal and backgrounds.

  4. Past Study - 2 • cms = 500 and 1000 GeV, MH = 100 ~ 130 GeV. • Extend Moretti’s study with parton showering, hadronization, particle decays by ISAJET. • Examine exclusive analysis with semileptonic and hadronic decay channels • Madgraphand HELAS are used for signal and BG generation. H. Baer, S. Dawson, L. Reina PRD 61,013002 Semileptonic channel Solid .. ttH signal Dash … ttg BG Num. of selected events, Semileptonic channel Num. of selected events, Hadronic channel

  5. Past Study - 3 Juste, G. Merino, hep-ph/9910301 Calculated Cross-sections • cms = 800 GeV, MH = 120 GeV. • MadGraph and HERAS are used for ME calculation of ttH and ttZ events. • Other backgrounds are generated by Pythia. • Fragmentation and hadronization by JETSET. • Tesla quick detector simulation is applied. • Exclusive analysis on semileptonic and hadronic modes. • Cuts applied on various kinematics and Neural-net output. • tt (includes ttg?) BG is large, ttZ and WW are not small. Semileptonic channel result hadronic channel result

  6. Past Study - 4 • Done only at cms=800 GeV. • Higgs mass 120 ~ 200 GeV. • Use TESLA detector simulation, • various cuts are applied. • CompHep and Pythia for signal • and BG generation. • Perform exclusive analysis : • H g bb , top decays semileptonically • H g bb , top decays hadronically • H g W+W-, two like-sign lepton + 6 jets • H g W+W-, one lepton + 8 jets • Resonant backgrounds (e+e-g qq, tt, • W+W-, ZZ,ttZ) are considered to be • dominant. • 6 fermion backgrounds (bbbbbb, • bbbbqq,bbbbtt, etc…) are simulated by • WHIZARD, but not precisely due to • limitation of CPU power. A. Gay, hep-ph/0604034

  7. Past Study – 4(H g bb top semileptonic channel) • Contribution from e+e-g tt is quite large even after the background rejection. Visible mass (GeV) Total multiplicity Njets Thrust Light jet mass (GeV) Heavy jet mass (GeV)

  8. As a summary … • All analyses have been done with exclusive method. Any difficulties on fermion counting method ? or just not yet done? • ttg will be a dominant BG, but ttZ, tt, WW will also be non-negligible BGs. • Cuts on bb di-jet mass, jet-energy and other kinematic parameters will work to efficiently reject the ttg BGs. • Other BGs (WWH, ZZH, …) may be negligible (even with fermion counting method?).

  9. BG cross-section by MadGraph(SM, cms = 500 GeV, MH = 120 GeV) • 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

  10. Plans • Complete listing and calculation of the backgrounds (also with cms = 550,600 GeV). • Check consistency with past studies. • Look at kinematic quantities at generator-level. • Pass the MadGraph+PYTHIA info to quick detector simulation.

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