TtH developments

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In this page, we review the latest status of ttH(H->bb) analysis.



People signed up for this group:

  • Jan Winter
  • Matt Schwartz
  • Jon Butterworth
  • Simon Dean
  • Stefano Pozzorini
  • Laura Reina
  • Sally Dawson
  • Nicola Giacinto Piacquiadio
  • Markus Warsinsky
  • Rohini Godbole
  • Samir Ferrag
  • Joey Huston
  • Ketevi Assamagan
  • Fawzi Boudjema
  • Stefan Dittmaer
  • Lorenzo Magnea
  • Fabio Maltoni
  • Fulvio Piccinini
  • Mario Campanelli


To strengthen the discrimination power either between the signal/background or between correct/incorrect ttH combinations, it has been suggested to investigate these observables:

  • spin correlations:
    • mttH signal and background
    • "Electroweak Symmetry Breaking at the LHC" (A. Djouadi, R.M. Godbole) Fig 43. shows differences between ttH mass for scalar and pseudoscalar bosons.
    • deltaphi (lepton, hadronic b)
    • E(hadronic b)/E(hadronic top) vs E(lepton)/(E(lepton)+E(b from leptonic top))
    • NB.. generator has to have the top decay products provided as part of the ME process (not evolved by parton shower) (see samples section)
  • four b-jet invariant mass to discriminate signal from background (doesn't suffer as badly from incorrect combinations)
  • mH vs mttH
  • mH vs pt(H)
  • b-jet energy in the hadronic top rest frame
  • b-jet energy in the leptonic top rest frame


It may be possible to use subjet techniques similar to those used in recent WH studies to reduce the number of ttbar combinations in each event. See Jet Substructure for some further discussion.

Action items: After the workshop, Simon will produce ttH and tt+jets background samples in Sherpa. These will be in HepMC format for a Rivet substructure analysis. Matt and others from Jet Substructure would like to use these events with highly-boosted tops and Higgs to identify observables that are sensitive to the top decay.

tTbB background

The recent NLO QCD study of a tTbB sample gave a k-factor of 1.8. It is possible to reduce this to 1.2 after applying a jet veto cut requiring no extra hard jets (pTjet < 50 GeV).

  • How would the k-factor be affected by a change in jet size? Suggestion: use separation of 0.4
  • What would be the effect on an experimental analysis of such a jet veto cut? Action item: apply higher pT cuts to Higgs b-jets, suggested: 50 GeV

a priori Higgs mass

There is a great deal of interest to see how the analysis is affected by assuming prior knowledge of the Higgs mass:

  • size of Higgs mass window
  • position of Higgs mass window (template method)
  • likelihood parameters using the Higgs mass

This would be more in line with a high-luminosity approach where Higgs mass has already been measured in channels with higher cross-section.

Fully leptonic ttbar decay

Fully leptonic ttH would have less problems with combinations, but more problems with low branching fraction (~5%) and greater uncertainties from missing ET.

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