Centre d'études et d'expertise sur les risques, l'environnement, la mobilité et l'aménagement

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We report the first measurements of inclusive W and Z boson cross sections times the corresponding leptonic branching ratios for pp collisions at √ s = 1.96 TeV based on the decays of the W and Z bosons into electrons and muons. The data were recorded with the CDF II detector at the Fermilab 4Tevatron and correspond to an integrated luminosity of 72.0 ± 4.3 pb −1 . We test e-µ lepton universality in W decays by measuring the ratio of the W → µν to W → eν cross sections and determine a value of 0.991 ± 0.004(stat.) ± 0.011(syst.) for the ratio of W −ℓ−ν couplings (gµ/ge). Since there is no sign of non-universality, we combine our cross section measurements in the different lepton decay modes and obtain σW ×Br(pp → W → ℓν) = 2.749 ± 0.010(stat.) ± 0.053(syst.) ± 0.165(lum.) nb and σ γ * /Z × Br(pp → γ * /Z → ℓℓ) = 254.9 ± 3.3(stat.) ± 4.6(syst.) ± 15.2(lum.) pb for dilepton pairs in the mass range between 66 GeV/c 2 and 116 GeV/c 2 . We compute the ratio R of the W → ℓν to Z → ℓℓ cross sections taking all correlations among channels into account and obtain R = 10.84 ± 0.15(stat.) ± 0.14(syst.) including a correction for the virtual photon exchange component in our measured γ * /Z → ℓℓ cross section. Based on the measured value of R, we extract values for the W leptonic branching ratio, Br(W → ℓν) = 0.1082 ± 0.0022; the total width of the W boson, Γ(W ) = 2092 ± 42 MeV; and the ratio of W and Z boson total widths, Γ(W )/Γ(Z) = 0.838 ± 0.017. In addition, we use our extracted value of Γ(W ) whose value depends on various electroweak parameters and certain CKM matrix elements to constrain the Vcs CKM matrix element, |Vcs| = 0.976± 0.030.