Uncertainties in the Determination of $|V_{cb}|$

Abstract

I discuss the theoretical uncertainties in the extraction of $|V_{cb}|$ from semilep\-to\-nic decays of $B$ mesons, taking into account the most recent theoretical developments. The main sources of uncertainty are identified both for the exclusive decay mode $B\to D^{\ast }\ell \bar{\nu }$ and for the inclusive channel $B\to X\ell \bar{\nu }$. From an analysis of the available experimental data, I obtain $|V_{cb}{|}_{\mathrm{excl}}=0.041\pm 0.003_{\exp }\pm 0.002_{\mathrm{th}}$ from the exclusive mode, and $|V_{cb}{|}_{\mathrm{incl}}=0.040\pm 0.001_{\exp }\pm 0.005_{\mathrm{th}}$ from the inclusive mode. I also give a prediction for the slope of the form factor $\mathcal{F}(w)$ at zero recoil, which is ${\hat{\varrho }}^2=0.8\pm 0.3$.

Comments: Proceedings of 1995 Moriond Conference on Electroweak Interactions and Unified Theories, 11 pages, 3 figures available as uu-encoded postscript files