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

1
ee- g ttHPast Experimental (simulation)
Studiesand BG cross-section by MadGraph

• Sep-27 2007 physics WG meeting
• S. Uozumi (Shinshu)

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Past Study - 1

• S. Moretti, Phys. Lett. B 452 (1999) 338

• A study concentrates on cms500 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
• (ee-gWW , W g Htb g HbbW
• or ee- g tb, t g tH).
• may contains top Yukawa coupling.

ttg
ttg g 4blnqq
ttZ
ttHg 4blnqq (solid)
ttZ g 4blnqq
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)
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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.
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Past Study - 2

• H. Baer, S. Dawson, L. Reina PRD 61,013002

• cms 500 and 1000 GeV, MH 100 130 GeV.
• Extend Morettis 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.

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
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Past Study - 4

• A. Gay, hep-ph/0604034

• Done only at cms800 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 WW-, two like-sign lepton 6 jets
• H g WW-, one lepton 8 jets
• Resonant backgrounds (ee- g qq, tt,
• WW-, 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.

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Past Study 4(H g bb top semileptonic channel)

• Contribution from ee- 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)
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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?).

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BG cross-section by MadGraph(SM, cms 500 GeV,
MH 120 GeV)

• ee- g ttg 33.7 fb
• ee- g ttg g ttbb 0.67 fb
• ee- g ttZ 1.07 fb
• ee- g WWH 5.69 fb
• ee- g ZZH 0.56 fb
• ee- g ttWW, ttZZ too small to calculate

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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 MadGraphPYTHIA info to quick detector
  simulation.