Measurement of W pair production in e+ e- collisions at 189-GeV

Abstract The production of W + W − pairs is analysed in a data sample collected by ALEPH at a mean centre-of-mass energy of 188.6 GeV, corresponding to an integrated luminosity of 174.2 pb −1 . Cross sections are given for different topologies of W decays into leptons or hadrons. Combining all final states and assuming Standard Model branching fractions, the total W-pair cross section is measured to be 15.71±0.34 (stat.) ±0.18 (syst.) pb . Using also the W-pair data samples collected by ALEPH at lower centre-of-mass energies, the decay branching fraction of the W boson into hadrons is measured to be B(W→hadrons)=66.97±0.65(stat.)±0.32(syst.)%, allowing a determination of the CKM matrix element | V cs |=0.951±0.030(stat.)±0.015(syst.).