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Exploring Top Quark Decay and Production at Fermilab User's Meeting

In this talk by Meenakshi Narain, detailed studies of thousands of top decays and production at Fermilab are discussed, examining top quark properties and its interactions with new physics scenarios.

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Exploring Top Quark Decay and Production at Fermilab User's Meeting

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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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