Improved Measurement of|Vcb|UsingB¯→D*ℓν¯Decays

We determine the weak coupling $|V_{cb}|$ between the $b$ and $c$ quarks using a sample of $3\times {10}^6$ $B\overline{B}$ events in the CLEO detector at the Cornell Electron Storage Ring. We determine the yield of reconstructed $\overline{B}\to D^{*}\ell \overline{\nu }$ decays as a function of $w$, the boost of the $D^{*}$ in the $B$ rest frame, and from this we obtain the differential decay rate $d\Gamma /dw$. By extrapolating $d\Gamma /dw$ to $w=1$, the kinematic end point at which the $D^{*}$ is at rest relative to the $B$, we extract the product $|V_{cb}|\mathcal{F}(1)$, where $\mathcal{F}(1)$ is the form factor at $w=1$. Combined with theoretical results for $\mathcal{F}(1)$ we determine $|V_{cb}|=0.0469\pm 0.0014\mathrm{(}\mathrm{s}\mathrm{t}\mathrm{a}\mathrm{t}\mathrm{)}\pm 0.0020\mathrm{(}\mathrm{s}\mathrm{y}\mathrm{s}\mathrm{t}\mathrm{)}\pm 0.0018\mathrm{(}\mathrm{t}\mathrm{h}\mathrm{e}\mathrm{o}\mathrm{r}\mathrm{)}$.