American Physical Society Meeting

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• The lepton jets channel
• Preselection
• SVT b-jet identification
• Backgrounds
• Summary and Outlook

American Physical Society Meeting April 18,
2005 Tampa, Florida
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The lepton jets channel
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Preselected Samples

• Used same preselection as in the topological
  analyses but with a lower jet pT threshold
• The analysis is done in all four jet multiplicity
  bins
• The first two bins are used as cross-checks of
  the background estimates and the last two to
  extract the cross section
• 1 and 2 tags channels kept separate (?SB)

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The Secondary Vertex Tagger
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Analysis Method

• Determine the number of preselected events as a
  function of the jet multiplicity for each
  background
• Parametrize b-tagging efficiency vs. pT and ? in
  data
• Parametrize the mistag-rate vs. pT and ? in data
• Determine the event tagging probabilities

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b-tagging efficiency

• The probability for a jet to be tagged (measured
  in data) is split into
• Probability for a jet to be taggable
  (taggability)
• Probability for a taggable jet to be tagged
  (tagging efficiency)

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Mistag Rate

• A tagged light jet is a mistag
• Mistags have two sources
• Misreconstruction and resolution effects
• In flight decays of light particles
• Mistags are estimated from negative tagging rates
  in data and corrected for
• Heavy flavor contamination (gluon spliting into
  heavy quark pairs)
• Missing contribution from long lived particles
  not completely removed by SVT

(0.85)
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Physics Backgrounds

• Wjets is the dominant background

• The number of preselected Wjets is obtained from
  the data (Matrix Method)
• The number of preselected events for other
  physics backgrounds are obtained from MC cross
  sections
• QCD was obtained directly from the tagged data
  sample

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Observed vs. Predicted number of tags
(Systematic uncertainties not shown)
(Systematic uncertainties not shown)
S/Bexp 16.9
S/Bexp 2.6

• ? lumi ? 360pb-1 (cross section not estimated
  yet)
• stt 7pb used for ttbar contribution
• Good background estimation (1 and 2 jet bins
  control samples)
• Top populates third and forth jet bins

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Summary

• Entering into a top quark precision measurement
  era at the Tevatron!
• Current measurement in this analysis (under
  publication process) is competitive and in
  agreement with the theory
• Working towards an improved measurement of this
  cross section
• Increased data set (from 230pb-1 to 360pb-1)
• Refine strategy to reduce limiting systematic
  uncertainties
• Jet Energy Scale, Jet ID, b-tagging efficiency in
  data, W flavor fractions

Based on 230pb-1
N. Kidonakis and R. Vogt, Phys. Rev. D 68 (2003)
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• Back up slides

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Top Quark Production and Decay
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Observed vs. Predicted number of double tags

• Orthogonal to single tag channels

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Observed vs. Predicted number of single tags

• ? lumi ? 360pb-1
• stt 7pb used for ttbar contribution
• Good background estimation (1 and 2 jet bins
  control samples)
• Top populates third and forth jet bins