TtH developments

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Current revision (12:05, 16 June 2009) (view source)
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In this page, we review the latest status of ttH(H->bb) analysis.
In this page, we review the latest status of ttH(H->bb) analysis.
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== Useful Links ==
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[http://cdsweb.cern.ch/record/1178698?ln=en SUSY'09 talk with details of Atlas ttH(H->bb) CSC study] (Catrin Bernius)
== Participants ==
== Participants ==
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* Fabio Maltoni
* Fabio Maltoni
* Fulvio Piccinini
* Fulvio Piccinini
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* Mario Campanelli
== Discriminators ==
== Discriminators ==
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* spin correlations:
* spin correlations:
** mttH signal and background
** mttH signal and background
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** [http://arxiv.org/abs/0901.2030 "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)
** deltaphi (lepton, hadronic b)
** E(hadronic b)/E(hadronic top) vs E(lepton)/(E(lepton)+E(b from leptonic top))
** E(hadronic b)/E(hadronic top) vs E(lepton)/(E(lepton)+E(b from leptonic top))
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* b-jet energy in the hadronic top rest frame
* b-jet energy in the hadronic top rest frame
* b-jet energy in the leptonic top rest frame
* b-jet energy in the leptonic top rest frame
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More about top polarisation:
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* [http://arxiv.org/abs/0901.2030 "Electroweak Symmetry Breaking at the LHC" (A. Djouadi, R.M. Godbole)] Fig 43. shows differences between ttH mass for scalar and pseudoscalar bosons.
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* [http://www.hep.ucl.ac.uk/~sdean/leshouches_toppol/toppol.pdf Presentation about top polarisation] (Rohini Godbole)
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* [http://www.hep.ucl.ac.uk/~sdean/leshouches_toppol/tt.pdf Parton-level plots from ttbar events] (Fabio Maltoni)
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* [http://www.hep.ucl.ac.uk/~sdean/leshouches_toppol/tth.pdf Parton-level plots from ttbarH events] (Fabio Maltoni)
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* [http://www.hep.ucl.ac.uk/~sdean/leshouches_toppol/tt-cuts.pdf Parton-level plots from ttbar events with cut] (Fabio Maltoni)
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* [http://www.hep.ucl.ac.uk/~sdean/leshouches_toppol/tth-cuts.pdf Parton-level plots from ttbarH events with cut] (Fabio Maltoni)
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(the cut requires the ttbar invariant mass to be below 400 GeV. This cuts out ~80% of the sample but should enhance polarisation effects)
== Subjet ==
== Subjet ==
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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 generator samples. See [[Jet Substructure]] for some further discussion.
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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 and plots.
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'''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 ==
== 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).
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).
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* How would the k-factor be affected by a change in jet size?
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* How would the k-factor be affected by a change in jet size? '''Suggestion: use separation of 0.4'''
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* What would be the effect on an experimental analysis of such a jet veto cut?
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* 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'''
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* Homework: provide NLO QCD study authors with a set of experimental parameters
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== a priori Higgs mass ==
== a priori Higgs mass ==

Current revision

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

Contents

Useful Links

SUSY'09 talk with details of Atlas ttH(H->bb) CSC study (Catrin Bernius)

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
  • Mario Campanelli

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
    • 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

More about top polarisation:

(the cut requires the ttbar invariant mass to be below 400 GeV. This cuts out ~80% of the sample but should enhance polarisation effects)

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. See Jet Substructure for some further discussion and plots.

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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