TtH developments

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(Discriminators)
(Fully leptonic ttbar decay)
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== Fully leptonic ttbar decay ==
== Fully leptonic ttbar decay ==
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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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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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* Link to Bonn thesis, Markus?
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Revision as of 15:04, 13 June 2009

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

Contents

Participants

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

Discriminators

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

Subjet

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.

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?
  • 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

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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