  A new precise measurement of |V_{cb}| and of the branching ratio BR(\bar{B^0}
-> D^{*+} \ell^- \bar{\nu_\ell}) has been performed using a sample of about
5000 semileptonic decays \bar{B^0} -> D^{*+} \ell^- \bar{\nu_\ell}, selected by
the DELPHI detector at LEP I by tagging the soft pion from D^{*+} -> D^0 \pi^+.
The results are:
  V_{cb}=(39.0 +/- 1.5 (stat.) ^{+2.5}_{-2.6} (syst. exp.) +/- 1.3 (syst. th.))
x 10^{-3}
  BR(\bar{B^0} -> D^{*+} \ell^- \bar{\nu_\ell})=(4.70 +/- 0.13 (stat.)
^{+0.36}_{-0.31} (syst. exp.))%
  The analytic dependences 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.

High Energy Physics - Experiment