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Probing the Top Quark Mass with Leptons: The Framework University of Athens

Probing the Top Quark Mass with Leptons: The Framework University of Athens. Costas Vellidis. Why measure the Top Mass. The Higgs mass is tied to m top and m W. QCD Production (~6pb) dominates at Tevatron: 85%: 15%:. proton. e-e(1/81). mu-mu (1/81). tau-tau (1/81).

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Probing the Top Quark Mass with Leptons: The Framework University of Athens

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  1. Probing the Top Quark Mass with Leptons: The Framework University of Athens Costas Vellidis

  2. Why measure the Top Mass The Higgs mass is tied to mtop and mW

  3. QCD Production (~6pb) dominates at Tevatron: 85%: 15%: proton e-e(1/81) mu-mu (1/81) tau-tau (1/81) e -mu (2/81) e -tau(2/81) mu-tau (2/81) e+jets (12/81) mu+jets(12/81) antiproton gluon tau+jets(12/81) jets (36/81) Top pair Production and Decay • W bosons decay either • hadronically or leptonically. • W decays define channel: • Dilepton: 11% • Lepton+jets: 44.5% • All-hadronic: 44.5% • Half-life of top: ~10-25s • Top decays before hadronizing!

  4. Measurements of the Top Mass hep-ex/0507091

  5. Sensitivity to the Top Mass The main sources of systematic error are associated with jets PROPOSAL (UoA CDF group)Seek variable(s) that: • does not depend on the jet energy scale • does not depend on b-tagging • it is the same for both the Dilepton and the Lepton+jets channels Such a variable can be the leptons (μ/e) PT/ET

  6. Leptons’ PT vs top mass after simulation (lepton+jets channel) PT sensitive to the top quark mass Fit of a straight line to the mean values gives slope: 0.15

  7. Shape of leptons’ PT distribution(lepton+jets) c = 20 GeV (the PT cut), b = 0.1 GeV (stiffness of the cut)

  8. Mass dependence of shape (lepton+jets) p+1= average number of leptons within a PT interval of length q q = average PT per lepton For signal f(pT) : For background g(pT) :

  9. Expected number of signal events Expected number of background events Total number of events in the PT histogram Typically fix , and fit μ, ν, Mtop Definition of likelihood

  10. The statistical error scales • with the square root of the • integrated luminosity • By the end of CDF Run II (8.5 fb-1 expected, 2008) should go down to: • 9 GeV using only l+jets data • 7 GeV using both ll & l+jets Maximum likelihood test fit(lepton+jets channel)

  11. Summary • The top mass analysis, using only lepton PT information in the ttbarDilepton & Lepton + Jets channels, looks promising • The lepton PT distribution is understood and its sensitivity to the top mass is demonstrated through the linear dependence of its shape parameters • A likelihood function is defined and a test fit at 340 pb-1 in the Lepton + Jets channel is absolutely consistent with the published top mass results and with our Monte Carlo results (shown in the next talk) • Statistical and systematic error studies are under way (they are disussed in the next talk)

  12. Strategy • Create MC histograms of the lepton PT for top pair events with different top mass per histogram • Create MC histograms of the lepton PT for the background in the dilepton channel (Drell-Yan, WW/WZ, Z→ττ, fakes) and in the lepton+jets channel (W+jets and non-W background) • Define a likelihood function using a suitable model of the PT distributions for the signal and for the background, and determine the input top mass by maximizing this function with respect to its free parameters

  13. = (mass scale,proton structure functions, radiation) • has similar dependences • is subject to the uncertainties in the SM cross sections, in the integrated luminosity and in the acceptance used to determine it Systematic Uncertainties Uncertainties in the measurement of the leptons’ PT/ET are expected negligible, but the shape parameters and the background depend on dynamical effects with potentially significant uncertainties introducing systematic errors to the Mtop value of maximum likelihood:

  14. Constrained likelihood

  15. Why measure the Top Mass The Higgs mass is tied to mtop and mW

  16. Higgs Mass Dependence of MW The dependence of MW upon mH is well-approximated by the following expression due to Degrassi et al [PL B418, 209 (1998)]

  17. Event Selection Lepton categories: CEM, CMUP, CMX,PHX (dilepton only)

  18. Dilepton MC event weighing • i counts dilepton categories • ni normalized number of events • nill number of selected events • ntot  total number of events in the sample • Li  integrated luminosity • σ cross section • εi  overall efficiency • (event vertex and trigger efficiency X reconstruction and ID scale factors) • fjets = 1.067 Njet scale factor if Njets>=2

  19. PT distribution for events normalized to 340pb-1 Nexp=18.2 events CDF: 17.2±1.4

  20. PT distribution for WW/WZ and Zττ background events normalized to 340pb-1 Nexp=1.6 events Nexp=0.8 events CDF: 1.6±0.3 events CDF: 0.8±0.2 events

  21. PT distribution for signal and WW/WZ & Zττbackground events normalized to 340pb-1 Nexp=18.2 events Nexp=2.4 events CDF exp. total background: 10.5±1.9 events

  22. Lepton+jets MC event weighing • i counts lepton categories • ni normalized number of events • nil+4j number of selected events • ntot  total number of events in the sample • Li  integrated luminosity • σ cross section • εi  overall efficiency • (event vertex and trigger efficiency X reconstruction and ID scale factors) • f = 0.956  common scale factor for all i

  23. PT distribution for events normalized to 340pb-1 Nexp=70.4 events CDF: 80.9±15.0 Mtop = 175 GeV

  24. PT distribution for signal and W+4jetsbackground events normalized to 340pb-1 Nexp=170.4 events Nexp=100.1 events CDF: 210

  25. Fermilab Main Injector Tevatron

  26. High Pt Physics At √s=1.96 TeV High Mass Physics • Top physics • EWK physics • B-Physics • QCD • Exotic We end up with e, γ, jets (partons), μ,missing ET (ν) We need a detector able to discriminate and measure the above 5 objects!!

  27. Functional schematic Muon chambers Hadron calorimeter g Electromagnetic calorimeter m+ q c c c General purpose detector e+ n 1.4 T Solenoid Time of Flight Drift Chamber Silicon Detector

  28. CDF detector

  29. CDF detector 1.4 T Solenoid Muon Chambers Wire Tracking Chamber Calorimeters CDF Silicon Tracking System

  30. 2 leptons with PT > 20 GeV, at least one tight lepton • At least 2 tight jets, |η|≤ 2.5 and ET ≥ 15 GeV • Zveto for events in 76 GeV < Mll < 106 GeV window • MET > 25 GeV • L-cut: MET> 50 GeV if Δφ(MET, lepton or jet) < 200 • H > 200 GeV • 2 leptons of opposite sign Dilepton Event Selection

  31. PT distribution for WW/WZ and Zττ background events normalized to 340pb-1 Nexp=2.4 events

  32. Leptons’ PT vs top mass dilepton events generated with Pythia LHC PT sensitive to the top quark mass Fit of a straight line gives slope: 0.21

  33. Estimation of the statistical error of the top mass (Tevatron) Expected statistical error in the top mass, as extracted from the PT spectrum of the two leptons in the dilepton channel, as a function of Luminosity L Top mass is linearly dependent on the <PT>  <PT>=λmtop+κ For TEVATRON

  34. Estimation of the statistical error of the top mass (LHC) Top mass is linearly dependent on the <PT>  <PT>=λmtop+κ For LHC

  35. Distributions of Leptons’ PTafter simulation Mtop = 130 GeV/c2, <PT> = 51.85 GeV/c Mtop = 180 GeV/c2, <PT> = 56.73 GeV/c Mtop = 230 GeV/c2, <PT> = 64.70 GeV/c Normalization 1

  36. Other kinematic variables vs top mass after simulation Again, the numbers in parton level 

  37. Other kinematic variables vs top mass events generated with Pythia Again, the numbers for 

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