Single Top search

1
Single Top search

• - Estimation of background rejection power with
  SJ tagger using Mistag Matrix

Contents
K. Nakamura Univ. of Tsukuba

• Motivation
• Current Study and CDF NOTE
• Signal/Background Sample

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Motivation

• Produced electroweakly coupling
• Direct access to W-t-b vertex
• ssingletopVtb2
• Top-polarization study and V-A structure of EW
  top interaction
• Background study for SM Higgs search
• Exactly the same final state as WH-gtWbb
• Background of all channels to use Wnjet
  background
• Probe b-quark PDF (t-channel)
• Non-SM phenomena
• Heavy W boson
• Anomalous W-t-b coupling

t-channel
s-channel
But
Cross section is small (40 of stt) Larger
background cause of W2jets bin
Not established a significant evidence yet
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Current Study and CDF NOTE
Event selection and MC validation

• Signal Acceptance and Monte Carlo based
  backgrounds (CDF 7863)
• Validation of single-top signal samples (CDF
  7701)

Anlysis with 0.7 fb-1 (CDF 8112)

• Non-W and Wnjets (n1,2,3) background estimation
• Neural network b-tagger (CDF 7816)
• Kinematics fitter for top quark reconstruction
  (CDF 749)
• Construct discriminates with Neural network
• with
  Likelihood ratio

Result
Unit pb Limit 95CL theory Likelihood Ratio Neural Network
t-channel 1.980.21 lt 3.1
s-channel 0.880.07 lt 3.2
ts comb. 2.860.28 lt 5.8 lt 3.4
Projections for Single Top Sensitivity
Phys. Rev. D 71, 012005 (2005)
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Last meeting result
WnP Background n2,3
W2P
13
W3P
30
Statistics of the background is small But we
confirmed 10 times rejection power
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Signal Sample
Generator Mad Event Event single top
s-channel LO Top Mass Mt175 GeV
Background Sample
Generator Alpgen pythia Event
W(-gte)nP W(-gtmu)nP (n
0,1,2,3,4)
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Mistag matrix
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W(-gte)4P
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Jet multiplicity distribution of b-tag performance
SecVtx
JetProb
19.2 64.7 13.6 2.1 0.3
Cross check

• Use Jproblt0.05 cuts for Jet Prob.

Jet multiplicity distribution after b tag (CDF
7863)
Good agreement !?
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Double tag SecVtx SecVtx SecVtx JetProb
About 68 statistics of the 2 tag events is
increased to use SJ tagging We can use 30 of
tight jets to combine ss sj tagging
gtgtgt about half of at least 1 secvtx tag
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WnP Background n2,3
W2P
13
W3P
30
Statistics of the background is small But we
confirmed 10 times rejection power
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Summery and Plan

• Double tag included sj tagging has potential to
  improve s/n ratio and significance.
• statistics of the signal is increased 1.68 x
  s-s tag
• We can use 30 of tight jets to combined s-s s-j
  tag
• About 10 times rejection power is estimated with
  WnP sample.
• Detail of signal selection will have to be
  confirmed.
• We will apply this double-tag method to other
  non-b background like 3jets .
• We will estimate signal significance and
  discovery potential as the function of
  luminosity

Because of just started , we have many TO DO
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Backup
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CEM ele ID
PHX ele ID
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m ID
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Gen info after geometrical cuts
muon
electron
lepton
L5 MET correction