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Top Physics at the Tevatron

Top Physics at the Tevatron. Mike Arov (Louisiana Tech University) for D0 and CDF Collaborations. Top physics overview. Discovered in 1995 by CDF ( 19 events ) and DO ( 17 events ) Has many unique properties: m top ~ gold atom Γ~1.4 GeV >> Λ QCD coupling to Higgs boson ~ 1.

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Top Physics at the Tevatron

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  1. Top Physics at the Tevatron Mike Arov (Louisiana Tech University) for D0 and CDF Collaborations

  2. 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

  3. Top physics Only selected new analyses are presented in this talk!

  4. Top production Top pair 15% 85% Single top s-channel t-channel

  5. Top Quark Decays

  6. 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 end • of 2010

  7. 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

  8. B-tagging Impact Parameter Tagging (IPT) Neural Network Tagging (NNT) Secondary Vertex Tagging (SVT) e, m Soft Lepton Tagging (SLT)

  9. B-tagging (continue) Good efficiency vs fake rate Works well with top quark

  10. Top Production Cross Section Summary

  11. Single Top s-channel t-channel Difiicault W background! Was challenging years after top pair discovery Small cross section B-tagging and multivariate analysis techniques were the key!

  12. Single Top Multivariate Analysis No single variable is sufficient! Boosted Decision Trees (BDT) Neural Networks (NN)

  13. Single Top Results Observation ! |Vtbf1L| = 0.88 ± 0.07

  14. Single Top Summary

  15. 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

  16. Top quark mass results (lepton+jets) Independent Jet Energy Scale (JES) measurement allows in-situ calibration

  17. Top Mass Summary 173.1 ±0.6 (stat) ±1.1 (syst) GeV/c2

  18. 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

  19. Asymmetry Results Afb= 12 ±8 (fit) ±1 (stat) Phys. Rev. Lett. 100 , 142002 (2008 ) Afb= 0.193 ±0.065 (stat) ±0.024 (syst)

  20. Spin Correlations k= -0.17 +0.64–0.53 k= 0.320 +0.545 –0.775

  21. Mass Difference Main motivation – check CPT Using matrix method in l+jets channel Likelihood function modified to allow for different top masses DMt= 3.8 ±3.7 GeV

  22. Search for Charged Higgs boson If H+ is lighter than top we can have the following scenarios:

  23. Search for Charged Higgs boson Leptophobic model Tauonic model

  24. 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 3 jets 4 jets

  25. Search for ttbar Resonances The limit is set using Mtt distributions For topcolor-assisted technicolor MZ' > 820 GeV (D0) and MZ' > 805 GeV (CDF)

  26. Summary • Top 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.

  27. Backup slides

  28. muon system shielding electronics D0 and CDF Detectors

  29. Experimental challenges of top quark physics • Jet Energy Scale • b-tagging • Limited statistics (less so as we collect more data) • Accurate background modeling (mainly W and QCD) • Luminosity measurement uncertainties

  30. Jet Energy Scale The associated statistical and systematic uncertainty is dominant one in top physics

  31. Resonance not observed

  32. Search for W' decaying to top and b Heavy W' can be observed in single top s channel The right-handed W' limit depends on the unknown mass of the right-handed neutrino, since when M(w'R) <M(nR) only hadronic decays of W are allowed. The following limits were set : • M(w'L) > 731 GeV • M(w'R) > 768 GeV for M(w'R) <M(nR) • M(w'R) > 739 GeV for M(w'R) >M(nR) Phys. Rev. Lett. 100 , 211803 (2008 )

  33. W helicity f0= 0.62 ±0.10 (stat) ±0.05 (syst) f+= -0.04 ±0.04 (stat) ±0.03 (syst) f0= 0.49 ±0.11 (stat) ±0.09 (syst) f+= 0.11 ±0.06 (stat) ±0.05 (syst) SM f0= 0.697±0.012 f+= 0

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