Single Top search

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Single Top search

• - Signal acceptance study using SJ B-tagging

K. Nakamura Univ. of Tsukuba
Contents

• Motivation
• Current Study and CDF NOTE
• Signal/Background Sample
• Lepton ID
• Jet Energy Correction
• MET Correction
• Event selection
• B-tagging
• Summery and Plan

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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
Projections for Single Top Sensitivity
Phys. Rev. D 71, 012005 (2005)
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Signal Sample
Generator Mad Event Event single top
s-channel LO Top Mass Mt175 GeV
Catalin Ciobanu 11/10/2005, Top Properties
Workshop
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Lepton ID
Standard tight lepton selection of leptonjet
group.
?Detail is in appendix
Electron
Etgt20 GeV Isolated Conversion Veto
Muon
Ptgt20 GeV/c Isolated Cosmic Veto
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Jet Energy Correction
Level4 Jet Energy Correction not to apply abs
correction
Etgt15 GeV, Eta lt 2.8
MET
Et
Et is corrected with lepton and Level4 jets
Phi
Etgt20 GeV
Et/Pt(n)
Phi/Phi(n)
L4 Jet 0.8 L5 Jet 1
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Event Selection
Cross check
This is t-channell result but
(96) (90) (25) (24) (24) (24) (23) (21)
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B-tagging
Performance of SecVtx and JetProb b-tagging
Number of events of under histogram include
Wnjet (ngt0) final state
For the statistics of the signal double SecVtx
tag is applied, about 70 statistics are
increased to use SJ tagging.
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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
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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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(No Transcript)
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m ID
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Gen info after geometrical cuts
muon
electron
lepton
L5 MET correction