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 th
e W boson has been studied. The ratio R-c(W) = Gamma (W --> cX)/Gamma(W -->
hadrons) has been measured from jet properties, lifetime information, and
leptons produced in charm decays. A value compatible with the Standard Mode
l expectation of 0.5 is obtained: R-c(W) = 0.481 +/- 0.042 (stat.) +/- 0.03
2(syst.). By combining this result with measurements of the W boson total w
idth and hadronic branching ratio, the magnitude of the CKM matrix element
IV,,I is determined to be /V-cs/ = 0.969 +/- 0.058. (C) 2000 Elsevier Scien
ce B.V. All rights reserved.