A measurement of vertical bar V-cb vertical bar using (B)over-bar(0)->D(*+)l(-)(v)over-bar(l) decays

The magnitude of the Cabibbo-Kobayashi-Maskawa matrix element V-cb has been measured using (B) over bar(0) --> D*(+)l(-)(v) over bar decays recorded on the Z(0) peak using the OPAL detector at LEP. The D*(+) --> D(0)pi(+) decays were reconstructed both in the particular decay modes D*(+) --> D(0)pi(+) and D*(+) --> D(0)pi(+)pi(0) and via an inclusive technique. The product of \V-cb\ and the decay form factor of the (B) over bar(0) --> D*(+)l(-)(v) over bar transition at zero recoil F(1) was measured to be F(1)\V-cb\ = (37.1 +/- 1.0 +/- 2.0) x 10(-3), where the uncertainties are statistical and systematic respectively. By using Heavy Quark Effective Theory calculations for F(1), a value of\V-cb\ = (40.7 +/- 1.1 +/- 2.2 +/- 1.6) x 10(-3)was obtained. where the third error is due to theoretical uncertainties in the value of F(1). The branching ratio Br((B) over bar(0) --> D*(+)l(-)(v) over bar) was also measured to be (5.26 +/- 0.20 +/- 0.46)%. (C) 2000 Published by Elsevier Science B.V. All rights reserved.