RevModPhys.84.1477】Tests of the standard electroweak model at the energy frontier

Is that the reconstructed mass of the two top quarks

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Unformatted text preview: of the spectrum. The impact of final-state radiation can be controlled by requiring exactly four reconstructed (good) jets in the event. For dilepton events, the number of measurements minus the number of constraints does not give enough information to fully determine the final-state kinematics, and one assumption must be made. A variety of methods are used including ME weighting and neutrino weighting. The ME weighting method (Kondo, 1988, 1991; Dalitz and Goldstein, 1992) is related to the general ME method described below (and also used for ‘ þ jets analyses). The neutrino weighting method (Abbott et al., 1998, 1999) is unique to dilepton events. In this method, an event weight is defined as a function of hypothesized top-quark mass Mt using a comparison of the measured ET to ETi values predicted for a set of possible 6~ 6~ neutrino pseudorapidity values ð1Þ , ð2Þ . Large weights cori i respond to situations in which the measured and predicted ET 6~ are similar and thus give a probability for different  values for the neutrinos in each event. The use of the ME approach has become widespread, especially for ‘ þ jets final states. It is used either as the final analysis variable used to determine the measured mass or to provide information used in joint likelihoods for determining the top mass. In this approach, the probability that the jet momenta, lepton momentum, and missing transverse en" ergy observed in a given event, assuming it arises from tt production and decay, is computed by (Abazov et al. (2008f) Ptt" ¼ 1ZX dðy; Mt Þdq1dq2fðq1 Þfðq2 ÞW ðy; xÞ N in which d is the differential cross section for production of the final-state partons in (momentum) configuration y for a given Mt , fðq1 Þ and fðq2 Þ are the parton density functions for the proton and antiproton, W ðy; xÞ is the transfer function for Hobbs, Neubauer, and Willenbrock: Tests of the standard electroweak model at . . . Pðx; Mt Þ ¼ AðxÞ½fPtt"ðx; Mt Þ þ ð1 À fÞPbkg ðxފ ∆ log(L) = 0.5 1 ∆ log(L) = 2.0 ∆ log(L) = 4.5 ∆JES (σc) 0.5 0 -0.5 -1 166 168 170 172 174 176 1507 178 2 M top (GeV/c ) FIG. 43 (color online). Contours of constant-log(L) in the Ájes  kjes À 1 vs Mt plane. A perfect a priori jet energy calibration used as input to this analysis results in kjes ¼ 1 corresponding to Ájes ¼ 0. From Aaltonen et al., 2009d. computing the probability that a partonic final state y gives the observed reconstructed final state x, and 1=N is a normalization factor equal to the expected observed cross section for a given Mt . For each event, this probability and the corresponding probability computed assuming the event is a background event Pbkg ðxÞ are combined to give an event probability as a function of top mass in which AðxÞ is a normalization factor incorporating accep" tance and efficiency effects and f is the fraction of tt events in the total sample. The overall normalization of P is forced to unity so that i...
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