Abstract
Two samples of exclusive semileptonic decays, 579 B 0 → D ∗+ℓ − ν ℓ events and 261 B 0 → D +ℓ − ν ℓ events, are selected from approximately 3.9 million hadronic Z decays collected by the ALEPH detector at LEP. From the reconstructed differential decay rate of each sample, the product of the hadronic form factor F (ω) at zero recoil of the D (∗)+ meson and the CKM matrix element | V cb| are measured to be F D ∗+ (1)|V cb | = (31.9 ± 1.8 stat ± 1.9 syst ) × 10 −3 , F D + (1)| V cb| = (27.8 ± 6.8 stat ± 6.5 syst) × 10 −3. The ratio of the form factors F D + (1) and F D ∗+ (1) is measured to be F D + (1) F D ∗+ (1) = 0.87 ± 0.22 stat ± 0.21 syst . A value of | V cb| is extracted from the two samples, using theoretical constraints on the slope and curvature of the hadronic form factors and their normalization at zero recoil, with the result | V cb| = (34.4 ± 1.6 stat ± 2.3 syst ± 1.4 th) × 10 −3. The branching fractions are measured from the two integrated spectra to be Br( B 0 → D ∗+ℓ − ν ℓ) = (5.53 ± 0.26 stat ±0.52 syst ) %, Br( B 0 → D ∗+ℓ − ν ℓ) = (2.35 ± 0.20 stat ± 0.44 syst ) %.
Published Version
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