The Top Quark Mass An Important thing to know.
Alcala, Carlos, Features Reporter has reference to this Academic Journal, PHwiki organized this Journal 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 t Z W b c s d u e e Particle Masses The St in addition to ard Model Why measure the Top Quark Mass Related to st in addition to ard model observables in addition to parameters through loop diagrams Consistency checks of SM parameters Precision measurements of the Mtop ( in addition to MW) allow prediction of the MHiggs Constraint on Higgs mass can point to physics beyond the st in addition to ard model Summer 2005
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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 in addition to 20:1 requiring 1 identified b tag Final State from Leading Order Diagram What we measure 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), in addition to 2 (2 b tags) 1 neutrino: over constrained Most precise Mtop measurements Final State from Leading Order Diagram What we measure 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
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 in addition to all methods -> precision Mtop Different statistical in addition to systematical sensitivities in each channel Other sources arise from the assumptions employed to infer Mtop: Initial state in addition to final state radiation Parton distribution functions b-jet energy scale Generators Background modeling in addition to composition b-tagging efficiency MC statistics Systematics dominated by the uncertainty on parton energies (Jet Energy Scale, JES) Jet Energy Scale Jet energy scale Determine the energy of the quarks produced in the hard scattered We use the Monte Carlo in addition to data to derive the jet energy scale Jet energy scale uncertainties Differences between data in addition to Monte Carlo from all these effects
In-situ Measurement of JES Additionally, we use Wjj mass resonance (Mjj) to measure the jet energy scale (JES) uncertainty Mjj Measurement of JES scales directly with statistics! Constrain the invariant mass of the non-b-tagged jets to be 80.4 GeV/c2 Data in addition to Monte Carlo b-jet pT ttbar pT W-jet pT Mttbar 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!
Mtop Lepton+Jets Results Detected Top C in addition to idate Silicon Detector Results Top Mass – Guessing Jets
Top Mass – Templates Run Monte carlo with various mass hypotheses. These are used as templates that can be compared to data using the c2 difference between data in addition to the template. Top Mass Background Templates Use W+Jet background with fake electron in addition to mistagged b to check that jet shapes are OK in MC. Then use MC to generate a background mass plot. Template Analysis Reconstructed mtop in addition to mjj from data are compared to templates of various true Mtop in addition to JES (jet energy uncertainty shift) using an unbinned likelihood Uses all four samples to increase sensitivity
Template Analysis Results Using 360 c in addition to idate 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! Matrix Element Analysis Technique Optimizes the use of kinematic in addition to dynamic in as long as mation Build a probability as long as a signal in addition to background hypothesis Likelihood simultaneously determines Mtop, JES, in addition to signal fraction, Cs: 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 in addition to neutrino solutions are taken into account Lepton momenta in addition to 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
Cross-check Monte Carlo with Data Compare Data in addition to Monte Carlo calculating the invariant mass of 2 in addition to 3 jets Signal probability evaluated at Mtop=174.5 GeV/c2 in addition to JES=1 in addition to using the most probable configuration Excellent agreement found between data in addition to Monte Carlo Results Using the 118 c in addition to idates in 680 pb-1 our Mtop is: with JES = 1.019 0.022 (stat) Better sensitivity than the previous world average! 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
Mtop All Jets Results 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 in addition to events ET/ ( ET) < 3 (GeV)1/2 ET 280 GeV nb-tag 1 Exactly 6 jets Ideogram method from the Delphi experiment as long as the W mass measurement, used in a Run II preliminary D0 as long as top mass measurement in lepton+jets channel Ideogram Overview Define a 2D event likelihood as Weight each combination with kinematical in addition to b-tagging in as long as mation: wi Extract from kinematical fit to mtop in addition to manti-top m1, m2, 1,2, 2 Scomb combinatorial background from Monte Carlo Sm calculated convoluting Briet-Wigners in addition to Gaussian resolution functions Template Shapes Template as long as combinatorial background Signal, correct combination Template as long as background Using the two fitted masses gives a good separation between signal in addition to background Results Using 310 pb-1 in addition to 290 c in addition to idates we measure First Tevatron Run II all jets Mtop measurement Systematically limited! Similar statistical sensitivity as the lepton + jets channel Summary of Mtop Results We compare (confidence in addition to consistency) in addition to combine (precision) Conclusions Present uncertainties on Mtop in addition to MW help constrain MHiggs to about 40% MHiggs/ MHiggs Best fit favors light MHiggs where CDF/D0 are sensitive where difficult as long as LHC Mtop will continue to shrink New CDF/D0 MW expected soon MW will also shrink
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