Measurement of|Vcb|and the Form-Factor Slope inB¯→Dℓ−

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 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.Received 27 April 2009DOI:https://doi.org/10.1103/PhysRevLett.104.011802©2010 American Physical Society