Top production and decay properties at the Tevatron

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Top productionand decay propertiesat
theTevatron

• Michele Weber
• Fermilab
• For the D0 and CDF collaborations

Theres more thanbuffaloes at Fermilab !
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top quark physics
Top Spin
W helicity
Pair production (QCD)
Top lifetime
Top Charge
Single top (EW)
Top Mass
Production kinematics
Top Spin Polarization
Resonance production
Rare/non SM Decays
t prime
Branching Ratios
Anomalous Couplings
New Physics
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Top quark production at 1.96TeV
Top quark pair production via strong interaction
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Cacciari etal, JHEP 0404068,2004
6.7 pb (1.96TeV, mt175GeV/c2)
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Single top quark production via weak interaction
Not discovered yet
s-channel 0.88pb
Sullivan, Phys.Rev.D70114012,2004
t-channel 1.98pb
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total recorded 1200/pb
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Top quark decay identification
All jet 46
t?Wb ?100
Need to reconstruct and identifyElectrons,
muons, jets, b-jetsand missing transverse energy

• decay product have
• good angular separation in the lab frame
• high transverse momentum

e/mu jets 29
dilepton (e/?) 4.5
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Dilepton cross section
low BG but low yield
gt15GeV
gt20GeV
Sample recorded on inclusivelepton triggers with
ET(l)gt18GeV
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Add leptontrack events

• Loosen the selection(one reconstructed letpton
  one track)
• Recover S/B with b-tagging
• Veto 2nd other flavour lepton(combination with
  e?)

ltrack
ltrack eµ
Compare to ee ?? e?
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Lepton jets channel
medium yield, medium BG Golden channel for
properties
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ljets with b-tagging
2-tags
1-tag and HTgt200GeV
Ultra-pure top sample
Relative systematic uncertainties
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All jet
High yield, high BG
Data with final selection (with btagging)
M(jj)
M(bjj)
Background From data
Background substracted
360/pb
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Probing the Wtb vertex

• t?Wb / t?Wq
• W helicity in top events
• single top

Anomalies New physics ?
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Probing the assumption

• (True in SM with three quark generations)

Measurement count b-jets. The number of b-jets
depends stronglyon R and the tagging efficiency.

• Result is obtained from a binned maximum
  likelihood fit to datafor Njet 3 and Njet 4
• Simultaneous fit to R and cross section

Br(t?Wb)1 and ?tt7 pb
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Result
The most precise measurement to date
hep-ex/0603002
Model independent cross section measurement
PRL 95, 102002
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W Helicity from t?Wb Decays

• Examines the nature of the tWb vertex,probing
  the structure of weak interactions at energy
  scales near EWSB
• Stringent test of SM and its V-A type of
  interaction.
• Uses boosted W from top decays

0
30
70
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Results
Mlb (ljets dilepton)
Update with respect to PRD 72, 011104 (2005)
Mlb lepton pt hep-ex/0511023
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EW top quark production(single top)
Not discovered yet
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Analyses
See also poster
use of kinematical distributions to separate
single-topfrom t-tbar and Wjets Different
approaches discriminant / NN / decision trees
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Results
Limits will hopefully not decrease,but the
signal significance increase
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Single top searchesprobing new physics
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Is the top the SM top ?

• charge
• lifetime

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Top charge
See also poster

• A most fundamental quantity characterizing a
  particle
• Possible alternative to 2/3e (D.Chang etal
  PRD59, 09153(99))
• Introduce an exotic 4th family (Q1,Q4)R, with
  charge (-1/3,-4/3)
• Q4 is the discovered top quark
• True top quark has a mass of 270 GeV and escaped
  detection

SM
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93.7 LEX lt Ldata
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top lifetime
Lepton jets channel with 1 tagged jet Primary
Vertex constrained by jets Measure the lepton
impact parameter
Likelihood fit
Maximum likelihood for c?top0 ?m
SM 3x10-10?m
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Is there more than the top ?

• t-prime
• resonamces

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Search for a t - gt Wb
Search for a heavy4th generation quark(He etal.
Hep-ph/0102144) Template fit in (HT, MT)
Lower limit on the t mass of 258GeV/c2 at 95
C.L. Expect m(t)gt300 GeV/c2with 2/fb, unless
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t-tbar resonances in ljets
Search for a resonance in the t-tbar invariant
mass spectrum
Result upper limits

• Model exclusion narrow leptophobic Z with
  G1.2MZ
• CDF exclude M(Z)lt725GeV/c2
• D0 exclude M(Z)lt680 GeV/c2

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Conclusions

• Top turns eleven, we are now in theprecision era
  of top physics
• Top production is consistent with the standard
  model expectation. There is still space for
  anomalies.
• Detailed studies of EW from the tWb vertex
• Single top (EW production) to be discovered
• Searches for exotics

Understanding top quark production and properties
will be crucial for success at LHC. What we
learn at the Tevatron, both physics and analysis
tools, extends directly to LHC!
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20 nations 92 institutions 700 physicists
12 nations 60 institutions 800 physicists

• 8 layer silicon
• 16 layers scintillating fibers
• 2T Solenoid
• CalorimeterCental EndCap
• 1.8T Toroid
• 3 layers muon scintillator drift tubes

• Silicon detector
• COT drift chamber
• Solenoid
• CalorimetersCentral, wall, plug
• Muon scintillator chamber

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Tevatron
Linac Booster
p-bar
Main Injector Recycler
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Layer 0 installed at DZero!
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Dilepton channel(s)

• Features
• Small Br
• Small background
• Selection
• Jets with ET gt 15GeV
• Two chargedopposite sign leptonspTgt15 GeV
• Or 1 lepton and one track
• Etmiss and additionalselection optimizedby
  channel
• Backgrounds
• WW/WZ, Z/?????ll
• fake Etmiss in DY or fake leptons in multijet

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All hadronic channel

• Features
• Large Br
• Large background (S/B1/300)
• Need b-jet tagging
• Selection
• At least six jets pTgt15 GeV
• 1 hard primary vertex
• gt3 jets assigned to it
• ?R(tagged jets)gt1.5
• Backgrounds
• multijet production

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Leptonjets channel

• Signature

• Features
• Relatively high Br (29)
• Manageable background
• Perfect for studies of top properties
• Selection
• One isolated pTgt20 GeV
• 3 jets with pTgt15 GeV
• 1 jet with b-tag
• ETmissgt20 GeV
• Backgrounds
• W jets
• Multijet

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topological X-section
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b-jet tagging
Both CDF D0 use Secondary Vertex b-tagging
algorithm to reduce the Wjet background for
top events (require tagged jets)

• b-quark lifetime c? 450?m
• ? B hadrons travel
• 3 mm before decay

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All jet
High yield, high BG
350/pb
NN HT plus 5 morevariables
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Discriminating variables
Top events are

• Energetic
• HT
• Central
• Centrality HT/H
• Spherical
• Aplanarity(large A ? spherical events)
• Sphericity(large S ? isotropic events)
• ??(l, ETMiss)
• kTmin
• measure of minimum jet pT relative to another

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Discriminant function
For uncorrelated variables
(Only Wjets used in thediscriminant as the
kinematicproperties of multijet are similar)
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Integrated Luminosity
Design
Base
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