A measurement of | Vcb| from [formula omitted

Abstract

From approximately 3 million hadronic decays of Z bosons recorded with the aleph detector at lep, a sample of 410 ± 32 B 0 → D ∗+ ℓ − ν ℓ candidates is selected, where ℓ is either an electron or a muon. The differential decay rate dΓ ( B 0 → D ∗+ℓ − ν ℓ) dω 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 ( ω = 1)| V cb| = (31.4 ± 2.3 stat ± 2.5 syst) × 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) × 10 −3. From the integrated s the measured branching fraction is Br( B 0 → D ∗+ ℓ − ν ℓ) = (5.18 ± 0.30 stat ± 0.62 syst ) %.