Measurement of the B → Dℓν branching fractions and form factor

Using a sample of 3.3 × 10⁶ B-meson decays collected with the CLEO detector at the Cornell Electron Storage Ring, we have studied B^- → D⁰ℓ^-ν and B⁰ → D⁺ℓ^-ν decays, where ℓ^- can be either e^- or μ^-. We distinguish B → Dℓν from other B semileptonic decays by examining the net momentum and energy of the particles recoiling against D - ℓ pairs. We find Γ(B → Dℓν) = (14.1±1.0±1.2)ns^-1 and derive branching fractions for B^- → D⁰ℓ^-ν and B⁰ → D⁺ℓ^-ν of (2.32±0.17±0.20)% and (2.20±0.16±0.19)%, respectively, where the uncertainties are statistical and systematic. We also investigate the B → Dℓν form factor and the implication of the result for |V_cb|.