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(q) over bar) = 67.13 +/- 0.37 (stat.) +/- 0.15 (syst.)%, from which the CKM matrix element \V-cs\ is determined to be 0.958 +/- 0.017 (stat.) +/- 0.008 (syst.).