Determination of the Form Factors for the Decay B0 --> D*-l+nu_l and of the CKM Matrix Element |Vcb|

Abstract

We present a combined measurement of the Cabibbo-Kobayashi-Maskawa matrix element $|V_{cb}|$ and of the parameters $ρ^2$, $R_1$, and $R_2$, which fully characterize the form factors of the $B^0 \to D^{*-}\ell^{+}ν_\ell$ decay in the framework of HQET, based on a sample of about 52,800 $B^0 \to D^{*-}\ell^{+}ν_\ell$ decays recorded by the BABAR detector. The kinematical information of the fully reconstructed decay is used to extract the following values for the parameters (where the first errors are statistical and the second systematic): $ρ^2 = 1.156 \pm 0.094 \pm 0.028$, $R_1 = 1.329 \pm 0.131 \pm 0.044$, $R_2 = 0.859 \pm 0.077 \pm 0.022$, $\mathcal{F}(1)|V_{cb}| = (35.03 \pm 0.39 \pm 1.15) \times 10^{-3}$. By combining these measurements with the previous BABAR measurements of the form factors which employs a different technique on a partial sample of the data, we improve the statistical accuracy of the measurement, obtaining: $ρ^2 = 1.179 \pm 0.048 \pm 0.028, R_1 = 1.417 \pm 0.061 \pm 0.044, R_2 = 0.836 \pm 0.037 \pm 0.022, $ and $ \mathcal{F}(1)|V_{cb}| = (34.68 \pm 0.32 \pm 1.15) \times 10^{-3}.$ Using the lattice calculations for the axial form factor $\mathcal{F}(1)$, we extract $|V_{cb}| =(37.74 \pm 0.35 \pm 1.25 \pm ^{1.23}_{1.44}) \times 10^{-3}$, where the third error is due to the uncertainty in $\mathcal{F}(1)$.