TtH developments

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Revision as of 14:38, 13 June 2009 by SimonDean (Talk | contribs)
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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

To strengthen the discrimination power between the signal and the background it has been suggested to investigate these observables:

  • mttH signal and background
  • top-antitop spin correlations:
    • Link to Rohini's talk
    • NB.. generator has to have the top decay products provided as part of the ME process (not evolved by parton shower) (see samples section)
    • deltaphi (lepton, hadronic b)
    • E(hadronic b)/E(hadronic top) vs E(lepton)/(E(lepton)+E(b from leptonic top))
  • four b-jet invariant mass to discriminate signal from background
 (doesn't suffer 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. Simon intends to study this further on some standalone samples.

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?
  • What would be the effect on an experimental analysis of such a jet veto cut?
  • Homework: provide NLO QCD study authors with a set of experimental parameters

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

  • Link to Bonn thesis, Markus?
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