Measurement of the $\overline{B}\to \mathit{Dl}\overline{\nu }$ Partial Width and Form Factor Parameters

We have studied the decay $\overline{B}\to \mathrm{Dl}\overline{\nu }$, where $l=e$ or $\mu$. From a fit to the differential decay rate $d\gamma /dw$ we measure the rate normalization $F_D\left(1\right)|V_{\mathrm{cb}}|$ and form factor slope ${\hat{\rho }}_D^2$, and, using measured values of ${\tau }_B$, find $\gamma (\overline{B}\to \mathrm{Dl}\overline{\nu })=(12.0\pm 0.9\pm 2.1)\mathrm{ns}{}^{-1\mathrm{}}$. The resulting branching fractions are $B({\overline{B}}^0\to D^{+}{l}^{-}\overline{\nu })=(1.87\pm 0.15\pm 0.32)\%$ and $B(B^{-}\to D^0{l}^{-}\overline{\nu })=(1.94\pm 0.15\pm 0.34)\%$. The form factor parameters are in agreement with those measured in $\overline{B}\to D^{*}l\overline{\nu }$ decays, as predicted by heavy quark effective theory.