Measurement of |V cs | using W decays at LEP2

Decays of W+/- bosons, produced at LEP2, have been used to measure the \V-cs\ element of the Cabibbo-Kobayashi-Maskawa matrix. Values for \V-cs\ were extracted both from the measured hadronic branching ratio of W+/- decays and by tagging the flavour of hadronic jets produced in W+/- decays. Applying the two methods to the data collected during 1996 at energies of 161 and 172 GeV, DELPHI obtains \V-cs\ = 0.91(-0.14)(+0.15)(stat) +/- 0.05(syst). (C) 1998 Elsevier Science B.V. All rights reserved.