1. e + e -  ttH Past Experimental (simulation) Studies and BG cross-section by MadGraph Sep-27 2007 physics WG meeting S. Uozumi (Shinshu)

2. S. Moretti, Phys. Lett. B 452 (1999) 338 Past Study - 1 A study concentrates on cms=500 GeV, Higgs mass 100 ~ 140 GeV, ttH  bbbbWW  bbbb l 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 -  W+*W, W + *  Htb  HbbW or e + e - g t*b, t*  tH). may contains top Yukawa coupling. Table of cross-sections (M H = 130 GeV, no cuts) ttg ttg  4bl qq ttH (dash) ttH  4bl qq (solid) ttZ Higgs Mass (GeV) ttZ  4bl qq ttg  4bl qq ttZ  4bl qq All ZbbWW  4bl qq All bbWWg  4bl qq ttH  4bl qq (solid) All bbWW and ttH  4bl qq (dash)

3. Past Study - 1 S. Moretti also demonstrates bb di-jet mass and jet energy are useful to reject the QCD and ttZ backgrounds. Solid … ttH Dash … ttZ Dot … ttg b-Jets are ordered by their energy bb di-met mass M ij (GeV) M 12 M 13 M 14 M 23 M 24 M 34 Jet energy E i (GeV) E1E1 E2E2 E3E3 E4E4 Especially M 34 and E 4 have the discrimination power for the signal and backgrounds.

4. Past Study - 2 H. Baer, S. Dawson, L. Reina PRD 61,013002 cms = 500 and 1000 GeV, M H = 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. Num. of selected events, Semileptonic channel Num. of selected events, Hadronic channel Semileptonic channel Solid.. ttH signal Dash … ttg BG

5. Past Study - 3 A.Juste, G. Merino, hep-ph/9910301 cms = 800 GeV, M H = 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. Calculated Cross-sections Semileptonic channel result hadronic channel result

6. Past Study - 4 A. Gay, hep-ph/0604034 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  bb, top decays semileptonically H  bb, top decays hadronically H  W + W -, two like-sign lepton + 6 jets H  W + W -, one lepton + 8 jets Resonant backgrounds (e + e -  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.

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

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, M H = 120 GeV) e + e -  ttg … 33.7 fb e + e -  ttg  ttbb … 0.67 fb e + e -  ttZ … 1.07 fb e + e -  WWH … 5.69 fb e + e -  ZZH … 0.56 fb e + e -  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.