W+W- production cross section and W branching fractions in e+e- collisions at 189 GeV

Abstract From a data sample of 183 pb −1 recorded at a center-of-mass energy of s =189  GeV with the OPAL detector at LEP, 3068 W-pair candidate events are selected. Assuming Standard Model W boson decay branching fractions, the W-pair production cross section is measured to be σ WW =16.30±0.34(stat.)±0.18(syst.) pb. When combined with previous OPAL measurements, the W boson branching fraction to hadrons is determined to be 68.32±0.61(stat.)±0.28(syst.)% assuming lepton universality. These results are consistent with Standard Model expectations.