Measurement of the e⁺e^-→W⁺W^- cross section and W decay branching fractions at LEP

Abstract

From a total data sample of 701.1 pb^-1 recorded with e⁺e^- centre-of-mass energies of $\sqrt{s} =$161–209 GeV with the OPAL detector at LEP, 11693 W-pair candidate events are selected. These data are used to obtain measurements of the W-pair production cross sections at 10 different centre-of-mass energies. The ratio of the measured cross sections to the standard model expectation is found to be: ${\text{data}}/{{\text{SM}}} = 1.002\pm0.011 ({\text{stat.}}) \pm0.007 ({\text{syst.}}) \pm0.005 ({\text{theory}})$, where the uncertainties are statistical, experimental systematics and theory systematics respectively. The data are used to determine the W boson branching fractions, which are found to be consistent with lepton universality of the charged current interaction. Assuming lepton universality, the branching ratio to hadrons is determined to be 67.41±0.37(stat.)±0.23(syst.)%, from which the CKM matrix element |V_cs| is determined to be 0.969±0.017(stat.)±0.012(syst.). The differential cross section as a function of the W^- production angle is measured for the qqeν and qqμν final states. The results described in this paper are consistent with the expectations from the standard model.