Imprecated, yet impeccable:: on the theoretical evaluation of Γ (B→Xclν)

We present a detailed evaluation of the total semileptonic B meson width in terms of \V-cb \ and heavy quark parameters (quark masses and the expectation values of local heavy quark operators). Special attention is given to perturbative corrections which can precisely be calculated in a scheme with a hard Wilsonian cutoff at a scale around 1 GeV appropriate for the OPE, and to the potential impact of higher-order power corrections. We point out that the latter require control over possible contributions from four-quark operators containing charm quark fields. Analytical expressions are given which allow evaluating the width with various choices of parameters; ready-to-use expressions showing the dependence on the heavy quark parameters are presented as well. We illustrate these results by commenting on how these parameters can be extracted and what accuracy is likely to be achievable in the near future. (C) 2003 Elsevier B.V. All rights reserved.