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Tevatron Top Physics

Tevatron Top Physics. Meenakshi Narain Brown University (for the D0 and CDF collaborations). Fermilab User’s Meeting – June 4, 2008. 13 years ago… …we observed a few handfuls of top quark decays. today… …we are performing detailed studies of 1000s of top decays. top at Fermilab.

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Tevatron Top Physics

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  1. Tevatron Top Physics Meenakshi Narain Brown University (for the D0 and CDF collaborations) Fermilab User’s Meeting – June 4, 2008

  2. 13 years ago… …we observed a few handfuls of top quark decays today… …we are performing detailed studies of 1000s of top decays top at Fermilab 4.2 fb-1 3.7 fb-1 Meenakshi Narain - Fermilab User's Meeting

  3. strong production cross section branching fractions mass couplings outline • new physics? • FCNC decays • tt resonances • tb resonances • H+ • …. • electroweak production • |Vtb| Meenakshi Narain - Fermilab User's Meeting

  4. t W W b H0 W W why is the top quark important? • most massive elementary particle • dominant contributor to radiative corrections • how is its mass generated? • topcolor? • does it couple to new physics? • massive G, heavy Z’, H+, …  mtop2  log(mH) Meenakshi Narain - Fermilab User's Meeting

  5. top-antitop production • strong interaction  top-antitop pairs •  = 7.6±0.6 pb (Kidonakis & Vogt, arXiv:0805.3844) • mt = 171 GeV, NNLO(approx)+NNNLL, CTEQ6M •  = 7.6 ±0.6 pb (Cacciari et al., arXiv:0804.2800) • mt = 171 GeV, NLO+NLL, CTEQ6.5 •  = 7.8 ±0.6 pb (Moch & Uwer, arXiv:0804.1476) • mt = 171 GeV, NNLO(approx.), CTEQ6.5 Meenakshi Narain - Fermilab User's Meeting

  6. tWb with B ≈100% Wqq with B ≈67 % Wℓ with B ≈11% e/ with B ≈17 % final state signatures for top-antitop pairs b-tagging standard model top decay primary vertex secondary vertex all jets 46% had+jets 10% dileptons 6% lepton+jets 34% had+e/μ 4% Meenakshi Narain - Fermilab User's Meeting

  7. why measure the ttbar cross section? • cross section analysis • basic understanding of signal and background necessary for further study • consistency between channels • decay branching fractions • are there non-standard decays? B(tH+b) = 0 B(tH+b) = 0.1 B(tH+b) = 0.2 B(tH+b) = 0.3 B(tH+b) = 0.4 B(tH+b) = 0.5 B(tH+b) = 0.6 all jets dileptons lepton+jets Meenakshi Narain - Fermilab User's Meeting

  8. ttbar cross section in dilepton channel • characteristics • small branching fraction • two neutrinos • kinematically underconstrained • signal:background = 3:1 • selection • two isolated leptons/lepton+track • 2 jets • missing pT • Z rejection in ee/ channels Meenakshi Narain - Fermilab User's Meeting

  9. ttbar cross section in dilepton channel • CDF (2 fb-1) • b-tag  = 9.0±1.1(stat)±0.7(syst)±0.5(lum) pb • no b-tag  = 6.8±1.0(stat)±0.4(syst)±0.4(lum) pb • D0 (1 fb-1) • dileptons  = 6.8+1.2-1.1(stat)+0.9-0.8(syst)0.4(lum) pb • lepton+track  = 5.1+1.6-1.4(stat)+0.9-0.8(syst)0.3(lum) pb • combined  = 6.2  0.9(stat) +0.8-0.7(syst)0.4(lum) pb Meenakshi Narain - Fermilab User's Meeting

  10. Meenakshi Narain - Fermilab User's Meeting

  11. interesting because of tH+b, H+ 3 types of hadronic  decays require 1 , 1 e/, ≥2 jets, missing pT 1 jet is b-tagged neural networks distinguish  decays from background 1 track em cluster 38% 1 track no em cluster 12% ≥2 tracks 15% ttbar cross section in  channels •  = 7.4+1.4–1.3(stat)+1.2–1.1(syst)±0.4(lum) pb (2.2 fb-1) • B(ttl) = 0.190.08(stat)0.07(syst)0.01(lum) pb (1 fb-1) Meenakshi Narain - Fermilab User's Meeting

  12. jet jet b-jet b-jet jet jet All-hadronic (BR≈46%) ttbar cross section in all-jets channel • characteristics • large branching fraction • no neutrinos • complete reconstruction • signal:background 1:16 • selection • 6-8 well separated jets • no significant miss pT • at least one b-tag • neural network • ET, event shape, angles • backgrounds • pretag data x tagging probability from 4-jet control region 1 fb-1 CDF PRD 76 072009  = 8.3±1.0(stat)+2.0-1.5(syst)±0.5(lum) pb Meenakshi Narain - Fermilab User's Meeting

  13. e,m n b-jet b-jet jet jet MET Lepton+jets (BR~34%) ttbar cross section in l+jets channel • characteristics • large branching fraction • one neutrino • kinematically overconstrained • signal:background = 1:2, 2:1(b-tag) • selection • one isolated lepton • 4 jets • missing pT Meenakshi Narain - Fermilab User's Meeting

  14. ttbar cross section in l+jets channel • extract top fraction using event topology • angles, momentum sums, and event shape variables • dominated by statistical uncertainties CDF (0.8 fb-1) neural network =6.00.6(stat)0.9(syst)0.3(lum) pb D0 (0.9 fb-1) likelihood discriminant =6.60.8(stat)0.4(syst)0.4(lum) pb Meenakshi Narain - Fermilab User's Meeting

  15. ttbar cross section in l+jets channel • count number of events with at least one b-tagged jet • smaller statistical uncertainty • large systematic uncertainty from jet energy calibration and b-tagging CDF (2 fb-1) =8.2±0.5(stat)±0.8(syst)±0.5(lum) pb =8.7±1.1(stat)+0.9-0.8(syst)±0.6(lum) pb =7.8±2.4(stat)±1.5(syst)±0.5(lumi) pb D0 (0.9 fb-1) =8.1±0.5(stat)±0.7(syst)±0.5(lum) pb Meenakshi Narain - Fermilab User's Meeting

  16. Meenakshi Narain - Fermilab User's Meeting

  17. implications of cross section • compare different channels • B(tWb)>0.79 @ 95% CL • B(tH+b)<0.35 @ 95% CL for mH+ = mW and H+cs • compare with theory • combine likelihood and b-tag cross section measurements • σtt = 7.62 ± 0.85 pb for mtop = 172.6 GeV • mt = 170 ± 7 GeV Meenakshi Narain - Fermilab User's Meeting

  18. single top production • electroweak production of top quarks • s channel (tb) ─ t channel (tqb) • event selection • 1 isolated e/ • missing pT • 2-4 jets, ≥1 b-tag NLO = 0.9±0.1 pb  = 2.0±0.3 pb PRD70 (2004) 114012 Meenakshi Narain - Fermilab User's Meeting

  19. single top production • D0 results (0.9 fb-1) • CDF results (2.2 fb-1) • = 4.7 ± 1.3 pb • significance: 2.3 σ (expected) • significance: 3.6 σ (observed) • PRL 98, 181802 (2007) PRD (accepted) • = 2.2 ± 0.7 pb • significance: 5.1 σ (expected) • significance: 3.7 σ (observed) Meenakshi Narain - Fermilab User's Meeting

  20. single top production • measure |Vtb| from total cross section • D0: |Vtb|>0.68 @ 95% CL CDF: |Vtb|>0.66 @ 95% CL • disentangle s and t channels Meenakshi Narain - Fermilab User's Meeting

  21. template fits mass estimator (eg best mt from kinematic fitter) fit probability density functions from simulated tt events generated to data event-by-event likelihood for each event determine likelihood as a function of mt (eg by integrating over LO matrix element) extract mass from peak of joint likelihood Event 1 Event 2 Event 3 top mass measurement Meenakshi Narain - Fermilab User's Meeting

  22. D0 (1 fb-1) compute weight curve as a function of top mass for each event template fit to mass distribution CDF (2 fb-1) selection uses evolutionary neural network that optimizes resolution compute event weight using LO matrix element dilepton channel matrix weighting 171.2±2.7(stat)±2.9(syst) GeV 173.7±5.4(stat)±3.4(syst) GeV Meenakshi Narain - Fermilab User's Meeting

  23. lepton+jets • matrix element analysis • integrate over LO matrix element to get likelihood for event as a function of top quark mass • in situ jet energy calibration using Wqq decay • peak of joint likelihood = top quark mass • CDF: 171.4±1.5(statjes)±1.0(syst) GeV (1.9 fb-1) • D0: 172.2±1.1(stat)±1.6(systjes) GeV (2.1 fb-1) Meenakshi Narain - Fermilab User's Meeting

  24. jet jet b-jet b-jet jet jet all jets (CDF) • kinematic fitter • leading 6 jets • jj/jjj masses, jet pTs • 2-dimensional template fit • top/W masses with smallest 2 mtop = 177.0 ± 3.7(statjes) ± 1.6(syst) GeV Meenakshi Narain - Fermilab User's Meeting

  25. combination for the first time m/m<1% Run II goal: m  1 GeV http://tevewwg.fnal.gov/top/ http://lepewwg.web.cern.ch/LEPEWWG/plots/winter2008/ Meenakshi Narain - Fermilab User's Meeting

  26. top quark couplings • if top plays a special role in ewk symmetry breaking its couplings to W bosons may differ from predictions • sm predicts V-A coupling at Wtb  helicity of W boson • F0 = 0.7, F = 0.3, F+ = 0.0 (longitudinal, left-handed, right-handed) • different distributions of * angle between lepton and top in W rest frame Meenakshi Narain - Fermilab User's Meeting

  27. D0 (1 fb-1) F0 = 0.42 0.17(stat) 0.10(sys) F+= 0.12  0.09(stat) 0.05(sys) CDF (1.9 fb-1) top quark couplings 68% CL 95% CL Phys Rev Lett 100, 062004 (2008) Meenakshi Narain - Fermilab User's Meeting

  28. quarks with charge 4/3e FB ttbar asymmetry 4th generation t’ quarks scalar top production charged Higgs bosons tb resonances ttbar resonances FCNC decays of top quarks  disfavored  consistent with sm  m > 284 GeV no evidence limits on H+ tb,tH+b searches for non-standard physics Meenakshi Narain - Fermilab User's Meeting

  29. tb resonances • vector resonance: W’tb • left-handed couplings • DØ include interference with SM W • right-handed couplings • decay to Rl/qq, depending on m(R) • lower limits on MW’: 731-825 GeV Meenakshi Narain - Fermilab User's Meeting

  30. D0 (2.1 fb-1) technicolor Z’tt Hill & Parke, PRD 49 (1994) 4454) CDF (1.9 fb-1) massive gluon Gtt tt resonances MZ’>760 GeV for Z’/MZ’ =1.2% Meenakshi Narain - Fermilab User's Meeting

  31. FCNC decays of top quarks • flavor changing neutral currents • highly suppressed in sm • select Z(ee/) + ≥4 jets • fit to B(tZq) < 3.7% @ 95% CL Meenakshi Narain - Fermilab User's Meeting

  32. conclusion • top physics has come a long way since 1995 • Tevatron is still the only place to do it • ttbar cross section measured to 11% • evidence for single top production • 5 this summer? • top quark mass measured to 0.8% • will reach uncertainties below 1 GeV • top properties and possible non-standard physics studies in great detail • in the last year: D0 7 papers and 13 theses • in the last year: CDF 8 papers and 16 theses • it still looks like top http://www-d0.fnal.gov/Run2Physics/top/ http://www-cdf.fnal.gov/physics/new/top/top.html Meenakshi Narain - Fermilab User's Meeting

  33. thank you

  34. MH+> mt  H+  tb tb resonance MH+< mt  t  H+b H+cs charged Higgs bosons Meenakshi Narain - Fermilab User's Meeting

  35. top quark charge • is it • tW+b (Qtop = 2/3 e) • tW-b (Qtop = -4/3 e) • Exotic model • doublet (–1/3e,–4/3e) ? • D. Chang et al., PRD59 (1999) 091503 • D0 PRL 98, 041801 (2007) • 4/3e excluded at 92% CL • fraction of exotic quark pairs < 0.80  (90% CL) • CDF result with 1.5/fb • p-value for SM: 0.31 • exotic model XM excluded with 87% CL Meenakshi Narain - Fermilab User's Meeting

  36. FB charge asymmetry • Asymmetry: • LO – no asymmetry • NLO – small (3-5%) asymmetry predicted in sm • new physics could lead to larger values (eg Z’) CDF unfold reconstructed AFB to go to parton level AFBpp = 0.17± 0.07(stat) ± 0.04(syst) • D0 AFB in parton rest frame: • AFB = 0.12±0.08(stat)±0.01(syst) • consistent with sm expectation Phys. Rev. Lett. 100, 142002 (2008) Meenakshi Narain - Fermilab User's Meeting

  37. t’ quark • 4th generation heavy quark • pair-produced via strong interaction • more massive than top • decays to Wb, Ws, Wd Mt’ < 284GeV at 95%C.L. Meenakshi Narain - Fermilab User's Meeting

  38. mass syst • CDF dilepton l+jets Meenakshi Narain - Fermilab User's Meeting

  39. xsec syst D0 l+jets b-tag kinematic likelihood Meenakshi Narain - Fermilab User's Meeting

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