A measurement of |Vcb| from

From approximately 3 million hadronic decays of Z bosons recorded with the ALEPH detector at LEP, a sample of 410 +/- 32 B0 -> D*+l-νl candidates is selected, where l is either an electron or a muon. The differential decay ratedΓ(B0 -> D*+l-νl)/(dω) from this sample is fitted, yielding a value for the product of the CKM matrix element Vcb and the normalisation of the decay form factor at the point of zero recoil of the D*+ meson F(ω = 1)Vcb = (31.4 +/- 2.3stat +/- 2.5syst) × 10-3. A value for Vcb is extracted using theoretical calculations of the form factor normalisation, with the result Vcb = (34.5 +/- 2.5stat +/- 2.7syst +/- 1.5theory) × 10-3. From the integrated spectrum, the measured branching fraction is Br(B0 -> D*+l-νl) = (5.18 +/- 0.30stat +/- 0.62syst)%.