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

For w e and w decays the d0 result abazov et al

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Unformatted text preview: W !  decays. The D0 result (Abazov et al., 2009a) uses R Ldt ¼ 1:0 fbÀ1 and results are reported for the W ! e decay mode only. Candidate events are selected by requiring 6 a single high-pT isolated charged lepton and large ET . Table II shows the kinematic selection requirements, event yields, and background fraction for the W event selections. The backgrounds include Z ! ‘‘ events in which one lepton escapes identification, WW diboson events, and misidentification backgrounds in which the lepton is either a jet misidentified as an electron or a muon from semileptonic decay of hadrons in which the rest of the associated hadronic jet is not reconstructed. An additional source of events are the sequential decays W !  ! e and W !  ! . The CDF analysis treats these as signal while the D0 analysis incorporates these into the background template distributions. Events / 0.5 GeV/c2 component of the neutrino along the beam direction cannot be " inferred in pp collision events, so the W invariant mass cannot be reconstructed from its decay products and other variables are used to determine the mass. Three variables are used: (1) the lepton (e or ) transverse momentum p‘ , (2) the T (inferred) neutrino transverse momentum p , and (3) the T qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi Events/0.5 GeV/c2 1482 2 0 -2 50 60 70 80 90 100 2 mT (GeV/c ) FIG. 4 (color online). The mT distributions for (a) the CDF W !  channel, (b) the CDF W ! e channel, and (c) the D0 W ! e channel. Hobbs, Neubauer, and Willenbrock: Tests of the standard electroweak model at . . . The in situ calibration of charged particle momenta (CDF) and calorimetric measurement of electron energy (CDF, D0) is of crucial importance to this result. The CDF analysis uses a calibration of the tracker momentum scale (p) determined from dimuon and dielectron decays of J= c , Ç, and Z particles. This calibration is then transferred to the calorimeter energy measurement (E) using the E=p ratio. A final improvement is made for the W ! e mode by incorporating an additional calorimeter calibration based on Z ! ee decays. The D0 analysis uses calorimeter energy measurements, and the calibration is based on the mass reconstructed in Z ! ee events and a detailed simulation of the calorimeter response. For both experiments, this calibration is the dominant source of systematic uncertainty. Other sources of systematic uncertainty arise from trigger efficiency, lepton identification efficiency, correlation (in)efficiency such as occurs when the hadronic recoil is near the charged lepton, backgrounds, electroweak, and strong contributions to the production and decay model and the parton distribution functions. The mT distributions for each channel are shown in Fig. 4, and the results from each channel and the combinations of the channels for each experiment are shown in Table III. The systemat...
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This document was uploaded on 09/28/2013.

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