Measurement of vertical bar V-cb vertical bar and the Form-Factor Slope in (B)over-bar -> Dl(-) (nu)over-bar(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 B⎯⎯⎯→Dℓ−ν⎯⎯ℓ decays based on 460×106 BB⎯⎯⎯ events recorded at the Υ(4S) resonance with the BABAR detector. B⎯⎯⎯→Dℓ−ν⎯⎯ℓ decays are selected in events in which a hadronic decay of the second B meson is fully reconstructed. We measure ℬ(B−→D0ℓ−ν⎯⎯ℓ)/ℬ(B−→Xℓ−ν⎯⎯ℓ)=(0.255±0.009±0.009) and ℬ(B⎯⎯⎯0→D+ℓ−ν⎯⎯ℓ)/ℬ(B⎯⎯⎯0→Xℓ−ν⎯⎯ℓ)=(0.230±0.011±0.011), along with the differential decay distribution in B⎯⎯⎯→Dℓ−ν⎯⎯ℓ decays. We then determine (1)|Vcb|=(42.3±1.9±1.4)×10−3 and ρ2=1.20±0.09±0.04, where (1) is the hadronic form factor at the point of zero recoil.