A first look at H

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A first look at H -gt ??
Catherine WrightUniversity of GlasgowGlasgow
Atlas Meeting19/01/06
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H -gt ??

• Ideal decay channel for low mass discovery.
• 100 lt mH lt 150 GeV
• If discovered via different channel, ideal for
  accurate mass measurement.
• Requires excellent calorimetry.
• Need good photon efficiency, high jet rejection.

The decay mechanism for H -gt??.
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H -gt ??
There are four main channels via which the higgs
is generated. The production mechanism studied
can have an effect on our ability to find the
higgs via H -gt ??
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Production Mechanism
Selection of production mechanism leads to
different triggers and event selection
requirements for H -gt ??.
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The Backgrounds
The backgrounds for this decay are different
depending on the production channel being
analysed.
Irreducible Background real ?? continuum from
quark bremsstrahlung, born and box
mechanism direct production. W ??, Z ??,
tt??, bb?? - associated production.
Reducible Background jet/?, e/ ? - for direct
production ?l/jet, ??/jet, ?/jet/jet,
l/jet/jet - for associated production
Need excellent background reduction algorithms!
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Initial Analysis
The significance of this channel was below 5? in
initial studies of only one production channel -gt
NOT a discovery channel!
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Combined Analysis
Researchers at Wisconsin focussing on this
channel and on combined production channel
analysis! In particular they are looking at H-gt??
jet(s).
Different MC generators are used to produce
various aspects of the signal and background.
e.g. MC_at_NLO used to generate g-g fusion events.
Events then face pre-selection cuts!
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Combined Analysis contd

• Currently
• Fixed jet rejection applied.

What are the effects of this analysis on the
significance of the H -gt?? channel?

• Results show not only VBF important but
  gg-fusion also significant.

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The Significance
This new combined analysis has lead to an
improvement in the significance for the channel.
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The Comparator

• Developed by Chris Collins-Tooth
• Designed to optimise, via ?2 analysis, the fast
  simulation forcing it towards the full
  simulation.
• Provides a set of parameter values that
  minimises ?2 for your data sets.

• Opposite
• Example of
• comparator run
• for photons.

Original Photon plot at low eta (?lt1,4)
Tuned Photon plot at low eta (?lt1,4)
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Future Analysis (??)

• Future analysis should include better
  statistical determination of combined
  backgrounds, via e.g. cousins-huygens
  approximation. Plus investigation into systematic
  errors in this channel required.
• Further studies of rejection of g/q initiated
  jets needed.
• Effects of pile-up on mass reconstruction at low
  luminosity.
• Use of Event Views in Analysis this is the
  future of data analysis and therefore H-gt??
  should move in this direction.
• Introduction of comparator for generating
  accurate, fast large backgrounds e.g. ??
  continuum.

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Conclusions

• Plan to investigate this channel further as a
  first year project and as part of a combined low
  mass Higgs analysis.
• There is still much to be done with this low
  significance channel.
• By using combined analysis methods the
  significance is raised above the all critical 5?
  level one can further extend this idea to
  include other decay channels!

Thank you!!