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Alain Bellerive University of Chicago Existing constraints on the |Vcs| element of the Cabibbo-Kobayashi-Maskawa (CKM) matrix are reviewed. In particular the determination of |Vcs| from D semileptonic decays, neutrino beam experiments, and the LEP Collaborations. Emphasis is given to the recent measurements of the partial decay width RcW = Gamma(W->cX)/Gamma(W->hadrons) at LEP2 where the fundamental coupling of the charm quark to the W boson is studied using the kinematic properties of final state particles in W decays. Decays of W bosons, produced at LEP2, can be exploited to investigate charm production from the measured hadronic branching ratio of the W boson or by tagging the flavour of hadronic jets produced in W decays. By measuring the hadronic branching ratio of the W boson and by setting other CKM elements and couplings of the W boson to leptons to the presently known values, one can therefore determine |Vcs|. Additional information can be obtained by tagging the flavour of jets produced in hadronic W decays. The flavour of primary quarks from W decays is heavily veiled in the process of hadronisation. Tagging the charm jets in the OPAL detector is based upon jet properties, lifetime information, and semileptonic decay products of the charm quark. Applying the two methods, measurement of the relative rate of hadronic W decays and the charm composition of these decays, on the data collected at Ecm 183 GeV and 189 GeV, OPAL is able to determine the CKM matrix element |Vcs| with really good accuracy. A measurement of RcW allows an indirect determination of |Vcs| but also a direct test of unitarity of the CKM matrix in three generations within the framework of the Standard Model. Future prospects for more precise experimental information from LEP2 and NuTeV will be discussed.
Monday, June 12th 2000, 15:30 |