Measurement of |Vcb| and the Form-Factor Slope in ¯¯¯B→Dℓ−¯νℓ Decays in Events Tagged by a Fully Reconstructed B Meson

Abstract

We present a measurement of the Cabibbo-Kobayashi-Maskawa matrix element | V cb | and the form-factor slope ρ 2 in ¯¯¯ B → D ℓ − ¯ ν ℓ decays based on 460 × 10 6 B ¯¯¯ B events recorded at the Υ ( 4 S ) resonance with the BABAR detector. ¯¯¯ B → D ℓ − ¯ ν ℓ decays are selected in events in which a hadronic decay of the second B meson is fully reconstructed. We measure B ( B − → D 0 ℓ − ¯ ν ℓ ) / B ( B − → X ℓ − ¯ ν ℓ ) = ( 0.255 ± 0.009 ± 0.009 ) and B ( ¯¯¯ B 0 → D + ℓ − ¯ ν ℓ ) / B ( ¯¯¯ B 0 → X ℓ − ¯ ν ℓ ) = ( 0.230 ± 0.011 ± 0.011 ) , along with the differential decay distribution in ¯¯¯ B → D ℓ − ¯ ν ℓ decays. We then determine G ( 1 ) | V cb | = ( 42.3 ± 1.9 ± 1.4 ) × 10 − 3 and ρ 2 = 1.20 ± 0.09 ± 0.04 , where G ( 1 ) is the hadronic form factor at the point of zero recoil.