Nonperturbative QCD contributions to the inclusive semileptonic decay of the $B$ meson consist of the dynamic and kinematic components. We calculate the decay width in an approach based on light-cone expansion and heavy quark effective theory, which is able to include both components of nonperturbative QCD contributions. The kinematic component results in the phase-space extension and is shown to be quantitatively crucial, which could increase the decay width significantly. We find that the semileptonic decay width is enhanced by long-distance strong interactions by $+(9\mathrm{}\pm 6)\%$. This analysis is used to determine the CKM (Cabibbo-Kobayashi-Maskawa) matrix element $|V_{\mathrm{cb}}|$ with a controlled theoretical error. Implications of the phase-space effects for the nonleptonic decay widths of $b$ hadrons are briefly discussed. The experimental evidence for the phase-space effects is pointed out.

• Received 19 February 1997

DOI:https://doi.org/10.1103/PhysRevD.56.2928