Measurement of W-pair production in e+e- collisions at centre-of-mass energies from 183 to 209 GeV

The W+ W- production cross section is measured from a data sample corresponding to a total integrated luminosity of 683 pb-1, collected by the ALEPH experiment at LEP at centre-of-mass energies from 183 to 209 GeV. Individual cross sections for the different topologies arising from W decays into leptons or hadrons, as well as the total W-pair cross section are given at eight centre-of-mass energies. The results are found to be in agreement with recently developed Standard Model calculations at the one percent level. The hadronic branching fraction of the W boson is measured to be B(W→q anti q)=67.13±0.37(stat.)±0.15(syst.)%, from which the CKM matrix element vertical stroke Vcs vertical stroke is determined to be 0.958±0.017(stat.)±0.008(syst.) (orig.)