W physics at LEP

After the first observations of W bosons in leptonic interactions, about 1000 WW candidate events per experiment have been collected at LEP2. This allows the measurement of the WW production cross section at different centre-of-mass $9 energies, as well as W decay branching fractions. The W hadronic branching fraction can be converted into a test of the unitarity of the CKM matrix, or into an indirect determination of the matrix element ¦V/sub cs/¦. A more direct $9 measurement comes from a charm tag performed on jets from W decays. The W mass has been measured via the cross section (in the threshold region) and the direct reconstruction of the W decay products, using different techniques to $9 account for the distortions due to experimental effects. The cross sections, together with distributions of W production and decay angles, are used to measure trilinear gauge boson couplings. (2 refs).