Measurement of Vcb from the decay process (B)over-bar0→D*+l-(ν)over-bar

A new precise measurement of \V-cb\ and of the branching ratio BR(<(Bover bar>(0)--> D(+*)l(-)<()over bar>(l)) has been performed using a sample of about 5000 semileptonic decays (B) over bar (0) --> D(*+)l(-)<()over bar>(l), selected by the DELPHI detector at LEP 1 by tagging the soft pion from D*+ --> D(0)pi (+). The results are: V-cb = (39.0 +/- 1.5 (stat.)(-2.6)(+2.5) (syst. exp.) +/- 1.3(ayst. th.)) x 10(-3). BR((B) over bar0 --> D(*+)l(-)<()over bar>(l)) = (4.70 +/- 0.13(stat.)(-0.31)(+0.36) (syst. exp.))%. The analytic dependencies of the differential cross-section and of the Isgur-Wise form factor as functions of the variable w = v(B)0 . v(D)* have also been obtained by unfolding the experimental resolution. (C) 2001 Published by Elsevier Science B.V.