A MEASURE VERTICAL-BAR-V-CB-VERTICAL-BAR FROM (B)OVER-BAR(0)-]D-ASTERISK+L-(NU)OVER-BAR(L)

From approximately 3 million hadronic decays of Z bosons recorded with the ALEPH detector at LEP, a sample of 410 +/- 32 ($) over bar B-0 --> D*(+)l(-)nu(l) candidates is selected, where l is either an electron or a muon. The differential decay rate d Gamma(($) over bar B-0 --> D*(+)l(-)nu(l))/d omega from this sample is fitted, yielding a value for the product of the CKM matrix element \V-cb\ and the normalisation of the decay form factor at the point of zero recoil of the D*(+) meson F(omega = 1)\V-cb\ = (31.4 +/- 2.3(stat) +/- 2.5(syst)) x 10(-3). A value for \V-cb\ is extracted using theoretical calculations of the form factor normalisation, with the result \V-cb\ = (34.5 +/- 2.5(stat) +/- 2.7(syst) +/- 1.5(theory)) X 10(-3) From the integrated spectrum, the measured branching fraction is Br(($) over bar B-0 --> D*(+)l(-)nu) = (5.18 +/- 0.30(stat) +/- 0.62(syst))%.