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Top physics overview
Discovered in 1995 by CDF (19 events) and DO (17 events)Has many unique properties:• mtop ~ gold atom• Γ~1.4
GeV>>ΛQCD• coupling to Higgs
boson ~ 1
Top quark mass is measured with <1% uncertainty
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Tevatron collider at Fermilab• 1.96 TeV p-anti p collider• 396 ns between bunches• Has delivered ~6 fb-1 of
data since 2002, and• Running smoothly:
expect ~10 fb-1 by endof 2010
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Top Production Cross Section in lepton +jets channel
Luminosity uncertainty reduced by normalizing to Z cross section
B-tagging is a powerful tool for top physics
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B-tagging
Impact Parameter Tagging (IPT)
Secondary Vertex Tagging (SVT)
Soft Lepton Tagging (SLT)
e,
Neural Network Tagging (NNT)
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Single Tops-channel
t-channel
Difiicault W background!Small cross section Was
challenging years after
top pair discovery
B-tagging and multivariate analysis techniques were the key!
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Single Top Multivariate Analysis
Boosted Decision Trees (BDT)
Neural Networks (NN)
No single variable is sufficient!
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Top quark mass measurement methods
• Template method – using MC templates with different masses do fit to top data
• Matrix method – using probability density:
Acceptance Matrix Element Transfer Function
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Top quark mass results (lepton+jets)
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Independent Jet Energy Scale (JES) measurement allows in-situ calibration
Measurement of the Forward-Backward Charge Asymmetry in Top-Antitop Production
N+ is the number of events where top has larger rapidity than antitop, while N- is the number of events where it is smaller
In LO QCD it is 0, but in NLO it isn't due to interference between diagrams like these
NN
NNAfb
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Asymmetry Results
tt YY tt YY
Phys. Rev. Lett. 100 , 142002 (2008 )
Afb= 0.193 ±0.065 (stat) ±0.024 (syst)
Afb= 12 ±8 (fit) ±1 (stat)
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Mass Difference
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tt
Main motivation – check CPT
Using matrix method in l+jets channel
Likelihood function modified to allow for different top masses
Mt= 3.8 ±3.7 GeV
Search for ttbar Resonances in the Lepton+Jets (D0) and All Hadronic (CDF) Final State
Invariant mass was plotted for candidate events Good agreement was observed and no resonant production signal
4 jets3 jets
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Search for ttbar Resonances
For topcolor-assisted technicolorMZ' > 820 GeV (D0) and MZ' > 805 GeV
(CDF)
The limit is set using Mtt distributions
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SummaryTop physics at Tevatron is diverse research field covering both SM and beyond SM physics.
In this talk I presented our last combined and most precise measurements of top pair and single cross section. And I also showed latest development on top mass and several properties measurements and searches.
Not all analyses could be shown. A lot more info can be found on the webpages of colaborations:
http://www-d0.fnal.gov/Run2Physics/top/top_public_web_pages/top_public.html
http://www-cdf.fnal.gov/physics/new/top/public_tprop.html
More exciting measurements and searches are to come.
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D0 and CDF Detectors
Central Calorimeter
Solenoid
Fiber Tracker
Silicon
muon system
shielding
electronics
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Experimental challenges of top quark physicsJet Energy Scale b-taggingLimited statistics (less so as we
collect more data)Accurate background modeling
(mainly W and QCD)Luminosity measurement
uncertainties
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Jet Energy Scale
The associated statistical and systematic uncertainty is dominant one in top physics 30
Search for W' decaying to top and b
Heavy W' can be observed in single top s channelThe right-handed W' limit depends on the unknown mass of theright-handed neutrino, since when M(w'R) <M(R) only hadronicdecays of W are allowed. The following limits were set :
M(w'L) > 731 GeV
M(w'R) > 768 GeV for M(w'R) <M(R)
M(w'R) > 739 GeV for M(w'R) >M(R)Phys. Rev. Lett. 100 , 211803 (2008 )
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