Measurement of |V_{cb}| and the Form-Factor Slope in B[over ¯]→Dℓ^{-}ν[over ¯]_{ℓ} 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 B̅ →Dℓ-ν̅ ℓ decays based on 460×106 BB̅ events recorded at the Υ(4S) resonance with the BABAR detector. B̅ →Dℓ-ν̅ ℓ decays are selected in events in which a hadronic decay of the second B meson is fully reconstructed. We measure B(B-→D0ℓ-ν̅ ℓ)/B(B-→Xℓ-ν̅ ℓ)=(0.255±0.009±0.009) and B(B̅ 0→D+ℓ-ν̅ ℓ)/B(B̅ 0→Xℓ-ν̅ ℓ)=(0.230±0.011±0.011), along with the differential decay distribution in B̅ →Dℓ-ν̅ ℓ 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.