A measurement of the rate of charm production in W decays

Abstract Using data recorded at centre-of-mass energies around 183 and 189 GeV with the OPAL detector at LEP, the fundamental coupling of the charm quark to the W boson has been studied. The ratio R c W ≡Γ ( W → c X )/Γ ( W → hadrons ) has been measured from jet properties, lifetime information, and leptons produced in charm decays. A value compatible with the Standard Model expectation of 0.5 is obtained: R c W =0.481±0.042 (stat.) ±0.032 (syst.) . By combining this result with measurements of the W boson total width and hadronic branching ratio, the magnitude of the CKM matrix element | V cs | is determined to be | V cs |=0.969±0.058.