Measurements of the Semileptonic Decays $\Bb\to D\ell\nub$ and $\Bb\to D^*\ell\nub$ Using a Global Fit to $D X\ell\nub$ Final States

Abstract

Semileptonic $\bar{B}$ decays to $DX\ell \bar{\nu }$ ($\ell =e$ or $mu$) are selected by reconstructing $D0\ell$ and $D^{+}\ell$ combinations from a sample of 230 million ${\rm Y}(4S)\to B\bar{B}$ decays recorded with the BaBar detector at the PEPII $e^{+}{e}^{-}$ collider at SLAC. A global fit to these samples in a 3-dimensional space of kinematic variables is used to determine the branching fractions $\mathcal{B}(B^{-}\to D0\ell \bar{\nu })=(2.34\pm 0.03\pm 0.13)$ and $\mathcal{B}(B^{-}\to D^{\ast 0}\ell \bar{\nu })=(5.40\pm 0.02\pm 0.21)$,where the errors are statistical and systematic, respectively. The fit also determines form factor parameters in a HQET-based parameterization, resulting in ${\rho }_{D}2=1.20\pm 0.04\pm 0.07$ for $\bar{B}\to D\ell \bar{\nu }$ and ${\rho }_{D^{\ast }}2=1.22\pm 0.02\pm 0.07$ for $\bar{B}\to D^{\ast }\ell \bar{\nu }$ These values are used to obtain the product of the CKM matrix element $|V_{cb}|$ times the form factor at the zero recoil point for both $\bar{B}\to D\ell \bar{\nu }$ decays, $\mathcal{G}(1)|V_{cb}|=(43.1\pm 0.8\pm 2.3)\times 10^{-3}$, and for $\bar{B}\to D^{\ast }\ell \bar{\nu }$ decays, $\mathcal{F}(1)|V_{cb}|=(35.9\pm 0.2\pm 1.2)\times 10^{-3}$.

18 pages, 5 figures, submitted to Physical Review D