Top Physics at the Tevatron

Mike Arov (Louisiana Tech University)

for D0 and CDF Collaborations

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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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Top physicsOnly selected new analyses are presented in

this talk!

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Top productionTop pair

85% 15%

Single top

s-channel

t-channel

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Top Quark Decays

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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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B-tagging (continue)

Good efficiency

vs fake rate

Works well with top quark

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Top Production Cross Section Summary

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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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Single Top Results

Observation ! |Vtbf1L| = 0.88 ± 0.07

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Single Top Summary

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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

Top Mass Summary

173.1 ±0.6 (stat) ±1.1 (syst) GeV/c2

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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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Spin Correlations

= 0.320 +0.545 –0.775

= -0.17 +0.64–0.53

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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 Charged Higgs boson

If H+ is lighter than top we can have the following scenarios:

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Search for Charged Higgs boson

Leptophobic model

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Tauonic model

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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Backup slides

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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

Resonance not observed

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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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W helicity

f0= 0.49 ±0.11 (stat) ±0.09 (syst)f+= 0.11 ±0.06 (stat) ±0.05 (syst)

f0= 0.62 ±0.10 (stat) ±0.05 (syst)f+= -0.04 ±0.04 (stat) ±0.03 (syst)

f0= 0.697±0.012f+= 0

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