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The Top Quark

The Top Quark. The Top Quark Mass An Important thing to know. The Top Quark. The top quark was discovered only 10 years ago Existence is required by the SM, but striking characteristics: its mass is surprisingly large Studied only at the Tevatron. The Standard Model. Particle Masses.

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The Top Quark

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  1. The Top Quark • The Top Quark Mass • An Important thing to know. B. Todd Huffman - Oxford

  2. The Top Quark • The top quark was discovered only 10 years ago • Existence is required by the SM, but striking characteristics: its mass is surprisingly large • Studied only at the Tevatron The Standard Model Particle Masses t Z W b c s d u   e   e B. Todd Huffman - Oxford

  3. Why measure the Top Quark Mass? • Related to standard model observables and parameters through loop diagrams • Consistency checks of SM parameters • Precision measurements of the Mtop (and MW) allow prediction of the MHiggs • Constraint on Higgs mass can point to physics beyond the standard model Summer 2005 B. Todd Huffman - Oxford

  4. Dilepton Channel • Branching fraction: 5% (lepton = e or ) • Final state: 2 leptons, 2 b quarks, 2 neutrinos • Combinatorial background: 2 combinations • 2 neutrinos: under constrained, kinematically complicated to solve Mtop • S:B = 2:1 and 20:1 requiring 1 identified b tag Final State from Leading Order Diagram What we measure B. Todd Huffman - Oxford

  5. Lepton+Jets Channel • Branching fraction: 30% (lepton = e or ) • S:B = 1:4 to 11:1 depending on the b-tagging requirement • Combinatorial background: 12 (0 b tag), 6 (1 b tag), and 2 (2 b tags) • 1 neutrino: over constrained • Most precise Mtop measurements Final State from Leading Order Diagram What we measure B. Todd Huffman - Oxford

  6. All Jets Channel • Branching fraction: 44% • Huge amount of background S:B = 1:8 after requiring at least 1 b-tag jet • Combinatorial background: 90 combinations • Backgrounds mainly from multi-jet QCD production Final State from Leading Order Diagram What we measure B. Todd Huffman - Oxford

  7. Top Quark Mass at CDF • Robust program of top quark mass measurements • Many measurements in all the different channels -> consistency • Different methods of extraction with different sensitivity -> confidence • Combine all channels and all methods -> precision B. Todd Huffman - Oxford

  8. Mtop • Different statistical and systematical sensitivities in each channel • Other sources arise from the assumptions employed to infer Mtop: • Initial state and final state radiation • Parton distribution functions • b-jet energy scale • Generators • Background modeling and composition • b-tagging efficiency • MC statistics • Systematics dominated by the uncertainty on parton energies (Jet Energy Scale, JES) B. Todd Huffman - Oxford

  9. Jet Energy Scale • Jet energy scale • Determine the energy of the quarks produced in the hard scattered • We use the Monte Carlo and data to derive the jet energy scale • Jet energy scale uncertainties • Differences between data and Monte Carlo from all these effects B. Todd Huffman - Oxford

  10. In-situ Measurement of JES • Additionally, we use Wjj mass resonance (Mjj) to measure the jet energy scale (JES) uncertainty Constrain the invariant mass of the non-b-tagged jets to be 80.4 GeV/c2 Mjj Measurement of JES scales directly with statistics! B. Todd Huffman - Oxford

  11. Data and Monte Carlo W-jet pT b-jet pT ttbar pT Mttbar B. Todd Huffman - Oxford

  12. In this Talk • Lepton + jets: Template analysis • Lepton + jets: Matrix Element • Lepton + jets: Decay Length • All Hadronic: Ideogram • Missing Di-leptons…cannot go into detail on everything! B. Todd Huffman - Oxford

  13. Mtop Lepton+Jets Results

  14. Detected Top Candidate Silicon Detector Results B. Todd Huffman - Oxford

  15. Top Mass - Guessing Jets B. Todd Huffman - Oxford

  16. Top Mass - Templates Run Monte carlo with various mass hypotheses. These are used as ‘templates’ that can be compared to data using thec2 difference between dataand the template. B. Todd Huffman - Oxford

  17. Top Mass – Background Templates Use W+Jet backgroundwith fake electron and mistagged b to check that jet shapes are OK in MC. Then use MC to generatea ‘background’ mass plot. B. Todd Huffman - Oxford

  18. Template Analysis • Reconstructed mtop and mjj from data are compared to templates of various true Mtop and JES (jet energy uncertainty shift) using an unbinned likelihood • Uses all four samples to increase sensitivity B. Todd Huffman - Oxford

  19. Template Analysis Results • Using 360 candidate events in 680 pb-1 we measure • Using in-situ JES calibration results in 40% improvement on JES Better sensitivity than the previous world average! B. Todd Huffman - Oxford

  20. Matrix Element Analysis Technique • Optimizes the use of kinematic and dynamic information • Build a probability for a signal and background hypothesis • Likelihood simultaneously determines Mtop, JES, and signal fraction, Cs: B. Todd Huffman - Oxford

  21. Matrix Element Analysis Technique • For a set of set measured variables x: • JES sensitivity comes from W resonance –this too is in the fit. • All permutations and neutrino solutions are taken into account • Lepton momenta and all angles are considered well measured • Background probability is similar, no dependence on Mtop W(x,y) is the probability that a parton level set of variables y will be measured as a set of variables x (parton level corrections) dnis the differential cross section: LO Matrix element f(q) is the probability distribution than a parton will have a momentum q B. Todd Huffman - Oxford

  22. Cross-check Monte Carlo with Data • Compare Data and Monte Carlo calculating the invariant mass of 2 and 3 jets • Signal probability evaluated at Mtop=174.5 GeV/c2 and JES=1 and using the most probable configuration Excellent agreement found between data and Monte Carlo B. Todd Huffman - Oxford

  23. Results • Using the 118 candidates in 680 pb-1 our Mtop is: with JES = 1.019  0.022 (stat) Better sensitivity than the previous world average! B. Todd Huffman - Oxford

  24. New technique – B Decay Length • The method has been published by C. Hill et al. at PRD 71, 054029 • B hadron decay length  b-jet boost  Mtop • Uses the average transverse decay length of the b-hadrons <Lxy> Relies on tracking, no JES and uncorrelated with other measurements B. Todd Huffman - Oxford

  25. Mtop All Jets Results

  26. All Jets • Main challenges in this channel: • Small signal fraction S:B = 1:8 after requiring at least 1 identified b-jet • Large combinatorial background: 90 combinations • Selection and events • ET/  ( ET) < 3 (GeV)1/2 • ET  280 GeV • nb-tag 1 • Exactly 6 jets • Ideogram method from the Delphi experiment for the W mass measurement, used in a Run II preliminary D0 for top mass measurement in lepton+jets channel B. Todd Huffman - Oxford

  27. Ideogram Overview • Define a 2D event likelihood as • Weight each combination with kinematical and b-tagging information: wi • Extract from kinematical fit to mtop and manti-top m1, m2, 1,2, 2 Sm calculated convoluting Briet-Wigners and Gaussian resolution functions Scomb combinatorial background from Monte Carlo B. Todd Huffman - Oxford

  28. Template Shapes Template for combinatorial background Template for background Signal, correct combination Using the two fitted masses gives a good separation between signal and background B. Todd Huffman - Oxford

  29. Results • Using 310 pb-1 and 290 candidates we measure • First Tevatron Run II all jets Mtop measurement • Systematically limited! Similar statistical sensitivity as the lepton + jets channel B. Todd Huffman - Oxford

  30. Summary of Mtop Results We compare (confidence and consistency) and combine (precision) B. Todd Huffman - Oxford

  31. CDF April’06 (750 pb-1) 2.6 Combining Mtop Results • Excellent results in each channel • Combine them to improve precision • Include Run-I results • Account for correlations • Use BLUE (NIM A270 110, A500 391) • Matrix Element analysis in lepton+jets not yet included. Working to understand statistical correlations with Template analysis B. Todd Huffman - Oxford

  32. Future • We surpassed our Run II goal of measuring to 3 GeV/c2 precision • Have made extrapolations based on present methods • Upper limit: Only (stat) improves with luminosity • Lower limit: Everything improves with luminosity • Reality: likely somewhere in between With full Run-II dataset CDF should measure Mtop to < 1% B. Todd Huffman - Oxford

  33. Conclusions • What has been shown. • First Run-II determination in all-jets channel • Multiple methods and channels • Observed consistency builds confidence • CDF combined • CDF should reach 1% precision with full Run-II data set • Tevatron combination better still B. Todd Huffman - Oxford

  34. We'll continue to squeeze SM, will it hold? Conclusions • Present uncertainties on Mtop and MW help constrain MHiggs to about 40%MHiggs/ MHiggs • Best fit favors light MHiggs • where CDF/D0 are sensitive • where difficult for LHC • Mtop will continue to shrink • New CDF/D0 MW expected soon... • MW will also shrink B. Todd Huffman - Oxford

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