Measurement of |Vcb| and the form-Factor slope in b̄→Dℓ- ν̄ℓ decays in events tagged by a fully reconstructed B meson

We present a measurement of the Cabibbo-Kobayashi-Maskawa matrix element |Vcb| and the form-factor slope ρ2 in B̄→Dℓ-ν̄ℓ decays based on 460×106 BB̄ events recorded at the Υ(4S) resonance with the BABAR detector. B̄→Dℓ-ν̄ℓ decays are selected in events in which a hadronic decay of the second B meson is fully reconstructed. We measure B(B-→D0ℓ-ν̄ℓ)/B(B-→Xℓ- ν̄ℓ)=(0.255±0.009±0.009) and B(B̄0→D+ℓ- ν̄ℓ)/B(B̄0→Xℓ-ν̄ℓ)=(0.230±0. 011±0.011), along with the differential decay distribution in B̄→Dℓ-ν̄ℓ decays. We then determine G(1)|Vcb|=(42.3±1.9±1.4)×10-3 and ρ2=1.20±0. 09±0.04, where G(1) is the hadronic form factor at the point of zero recoil.