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Top physics at CDF

Top physics at CDF. "New Developments of Flavor Physics" March 9 th , 2009. Koji Nakamura on behalf of CDF collaboration. Top Quark at Tevatron. What is top quark? Evidenced in 1994 by CDF, discovered in 1995 by Tevatron

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Top physics at CDF

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  1. Top physics at CDF "New Developments of Flavor Physics" March 9th, 2009 Koji Nakamura on behalf of CDF collaboration

  2. Top Quark at Tevatron • What is top quark? • Evidenced in 1994 by CDF, discovered in 1995 by Tevatron • The heaviest quark so far. The Mass is about 172 GeV. • Now We have much more data to analyze top quark properties. 24 Aug, 2008 Record : 3.8 fb-1 Good Data: 3.2 fb-1

  3. Top Quark at Tevatron • What is top quark? • Evidenced in 1994 by CDF, discovered in 1995 by Tevatron • The heaviest quark so far. The Mass is about 172 GeV. • Now We have much more data to analyze top quark properties. Top Quark properties in pair production Production Cross Section Fwd-Bwd Asymmetry Production Mechanism Mass Charge • New Physics • FCNC • ttbar resonance • charged Higgs • …… W helicity

  4. Top Quark at Tevatron • What is top quark? • Evidenced in 1994 by CDF, discovered in 1995 by Tevatron • The heaviest quark so far. The Mass is about 172 GeV. • Now We have much more data to analyze top quark properties. Single top production is allowed in SM ~ 2.9 pb ~ 6.7 pb 30% : 70%

  5. Singletop production

  6. Both CDF and D0 Submitted to PRL CDF Observation Lumi : 3.2 fb-1 Expected : 5.9 σ Observed : 5.0 σ arXiv.org:0903.0885 DØ Observation Lumi : 2.3 fb-1 Expected : 4.5 σ Observed : 5.0 σ arXiv.org:0903.0880

  7. Why Single Top Quark? Production rate is proportional to |Vtb|2 st = (1.98 ± 0.25) |Vtb|2pb ss = (0.88 ± 0.11) |Vtb|2pb Top Polarization study Single top quarks are 100% polarized in SM Can test this with angular distribution of top decay Probe Non Standard Model phenomena Can search for heavy W’ boson or H± Technical Motivation Test of the methodology for Higgs search (the same final state as the WHlνbb signal)

  8. 2 or 3 high Pt jets (Pt>20 GeV) difficulty Event topology Singletop production with decay into lepton + 2 jets final state One high Pt lepton (Pt>20 GeV) Background (at least 1 b-tag) Large Missing Energy (Et>25 GeV) Singletop Signal is hidden under the huge bkg  Multivariate analyses are needed Top pair Dominant process of 4 jets bin counting method is possible

  9. Analysis strategy Signal Model Background Model CDF Data Set Blind analysis Event Selection Lepton Trigger Event Met + Jets Trigger Event Non triggered lepton No lepton Multivariate Analysis Split in sub set of different purity Lep+jets Neural Network Multivariate Analysis Likelihood Function Neural Network Cross section measurement Discriminant |Vtb| measurement Boosted Decision Tree Matrix Element Significance and xsec limit

  10. Likelihood Analysis Used projective likelihood function to combine the separation power of several variables. t-channel optimized analysis s-channel optimized analysis 2 b-tag events Only Example of input variables Example of input variables pT Mlνb Q*η HT

  11. Result of Likelihood Analyses t-channel optimized analysis s-channel optimized analysis 2 b-tag events Only s- and t-channel are the signal s-channel is the signal Expected significance: 4.1 σObserved significance: 2.4 σ Expected significance: 1.1 σObserved significance: 2.0 σ

  12. Combination of Likelihood Analyses To obtain s- and t-channel cross section in ss-st plane, We perform s- and t-channel cross section fit simultaneously. Combine following 2 analyses: 1-b-tag events -- optimized to t-channel 2-b-tag events -- optimized to s-channel

  13. Matrix Element Analysis Using Matrix Element information to calculate probabilities for seven different underlying processes: s-channel, t-channel, Wbb, tt, Wcc, Wc+jet and Wgg.

  14. Result of ME Analysis Expected significance: 4.9 σObserved significance: 4.3 σ

  15. The other MV Techniques Neural Network analysis Boosted Decision Tree analysis Sequence of binary splits using the discriminating variable which gives best sig-bkg separation. An orthodox NN analysis using Neuro Bayes Program 18-25 variables are used

  16. Result of NN and BDT analyses Neural Network analysis Boosted Decision Tree analysis Expected significance: 5.2 σObserved significance: 3.5 σ Expected significance: 5.2 σObserved significance: 3.5 σ

  17. Combination : 5 lep+jets analysis Discriminant outputs from analyses (LFT, LFS, ME, NN, BDT ) are combined into a single, more powerful super discriminant (SD) using neural networks(NEAT). Expected significance: > 5.9 σObserved significance: 4.8 σ

  18. MET+jets without lepton channel Using no Lepton events by MET+jets Trigger. Independent sample from lepton+jets analysis. Using NN based event selection and NN based discriminant. Challenging!! Huge QCD background… Expected significance: 1.4 σObserved significance: 2.1 σ

  19. CDF Combination and Singletop Conclusion Finally, we combined Super Discrimant analysis and no Lepton analysis. Expected significance: > 5.9 σObserved significance:5.0 σ Cross section: |Vtb| calculation: Assuming no anomalous coupling |Vtb|=0.91± 0.11 (exp.) ± 0.07 (theory) |Vtb|>0.71(95% CL)

  20. ttbar properties L>=2.7 fb-1 result only (second half of 2008 and 2009) • Top Quark Mass Measurement • Top Quark production cross section • W helicity • Forward Backward asymmetry • ttbar production mechanism • Search for the FCNC top decay • Search for the stop Mimicking Top Event Signatures • Search for charged higgs in top decay • Search for the t’ quark • …… backup

  21. Top Mass measurement Combination • Most of analysis fit the top quark mass • with in-situ JES systematic. • The uncertainty of the top mass result • is already systematic dominant. • 0.85% precision 10% improved • We need reconsidering systematics. M top = (172.6 ± 0.9stat ± 1.2syst) GeV/c 2 e.g. New Systematic Uncertainty Color Reconnection: A Variation of the Phenomenological description of color reconnection between final state particles. Added here for the First Time !!

  22. Top Mass measurement New Result Template Method 3.0fb-1 : l+jets Matrix Element 3.2fb-1 ΔJES = 0.40 ± 0.26 σ Mtop = 171.8 ± 1.5 (stat.+JES) ± 1.1 (syst.) GeV/c2 All Had. 2.9fb-1 : templatewith NN selection Mtop = 171.8 ± 0.9 (stat.) ± 0.7 (JES) ± 1.1 (syst.) GeV/c2 Lepton Pt 2.7 fb-1 Mtop = 174.8 ± 1.7(stat.) ± 1.9(syst.) GeV/c2 M top = (172.1 ± 7.9stat ± 3.0syst) GeV/c 2

  23. Top Cross section Combination @Mtop=175 GeV Di-lepton : 2.8 fb-1 σpre = 6.7 ± 0.8stat ± 0.4syst ± 0.4lumi pb. σtag = 7.8 ± 0.9stat ± 0.7syst ± 0.4lumi pb. Lepton+jets with NN : 2.8 fb-1 Uncertainty is dominated by Luminosity Using ratio of σttbar/σZ 6%(lumi)->2%(theory) σttbar = 7.08 ± 0.38 (stat) ± 0.36 (syst) ± 0.41 (lumi) pb

  24. Following pages describe more detail http://www-d0.fnal.gov/Run2Physics/top/ http://www-cdf.fnal.gov/physics/new/top/top.html

  25. Backup

  26. Top Quark Decay Product all jets 46% had+jets 10% dileptons 6% lepton+jets 34% had+e/μ 4%

  27. Jet Clustering and energy correction Clustering Summing tower energies in ΔR( ) =0.4 Correction Relative correction Minimum bias correction Absolute value correction Underling event correction Out of cone correction

  28. SM |Vtb|<1 New Physics Phenomena in ss-st plane << SM H±,W’ (+)

  29. S-channel optimization search It is possible to search s-channel using 2-b-tag information Sensitive to the new physics mainly theory with extra boson(W’,H±) Exactly the same final state as: WH->lνbb (Golden channel at Tevatron) It is difficult to search s-channel at LHC because…

  30. Background Estimation (non W) QCD(nonW) Modeled by - failed electron - non isolated muon - jet trigger event MC based fixed W+jets Pre-b-tag events 2b-tagged events b-tagging W+jets : mistag weight W+bb, W+cc : HF fraction data QCD(nonW) x mistag weight Missing Et

  31. The number of event prediction

  32. Acceptance Gain for Muon Non-triggerd muon in Met+2Jets Trigger Lepton trigger requires CMU&CMP (CMUP) or CMX -> add CMU only, CMP only and so on… Muon Trigger event Single top @ CDF Acceptance +30% Significance +15%

  33. Systematic Uncertainty

  34. Top Mass measurement with in-situ W->jj JES calibration Template Method Mtop Mjj 1 tag 2 tag Mtop = 171.8 ± 1.5 (stat.+JES) ± 1.1 (syst.) GeV/c2 Matrix element (Multi-variate) Method ΔJES = 0.40 ± 0.26 σ Mtop = 171.8 ± 0.9 (stat.) ± 0.7 (JES) ± 1.1 (syst.) GeV/c2

  35. Top Mass : Lepton Pt 2.7 fb-1 Muon data Electron data M top = (172.1 ± 7.9stat ± 3.0syst) GeV/c 2

  36. Top Mass : All hadronic 2.9 fb-1 1 tag 2 tag Mtop Mjj Mtop = 174.8 ± 1.7(stat.) ± 1.9(syst.) GeV/c2

  37. Summer 2008 Tevatron Future Precision & EWK fit.

  38. ttbar cross section using Ratio σttbar/σZ σ ttbarmeasured =1/R x σZtheory σZtheory = 251.3 ± 5.0 (sys) pb σttbarmeasured = 7.08 ± 0.38 (stat) ± 0.36 (syst) ± 0.41 (lumi) pb σzmeasured=  253.27 ± 1.01(stat) +4.4-4.6 (sys) +16.63-13.71 (lumi) pb 1/R = σZ /σttbar =  36.47 +2.06-2.29 (stat) +1.88-1.96(sys) σ ttbarmeasured =6.89 ± 0.41(stat) +0.41-0.37(sys) ± 0.14 (theory) pb

  39. W helicity 1.9 fb-1 the angle between the lepton as measured in the W rest frame and the W boson as measured in the top rest frame

  40. cos θ* template fit method F+ = -0.04 ± 0.04(stat) ± 0.03(syst) F0= 0.59 ± 0.11(stat) ± 0.04 (syst) F+ < 0.07 @ 95% C.L. Matrix Element method Assuming f+=0 f0 = 0.637 ± 0.084 (stat) ± 0.069 (syst)

  41. Forward Backward Asymmetry 1.9 fb-1 Slightly positive Afb Slightly negative Afb

  42. ttbar production mechanism 2.0 fb-1 Azimuthal plane P P l  l gg fusion qq annihilation g Spin g q Spin q parallel spin state anti-parallel spin state J = 1 Jz = 1 J = 0 Jz = 0 1.0 fb-1 Combination Fgg=0.53+0.35-0.37(stat.)+0.07-0.08(syst.) Fgg = 0.07+0.15-0.07(stat+sys)

  43. Search for the FCNC top decay 1.9 fb-1 Searching t→Zq vertex in top decay Br(t→Zq) < 3.7 %

  44. Search For Pair Production of Stop Quarks Mimicking Top Event Signatures Similar decay product as ttbar

  45. etc…… A Search for charged Higgs in lepton+jets tt-bar events using 2.2 fb-1 of CDF data Search for Heavy Top t'->Wq In Lepton Plus Jets Events in 2.8 fb-1

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