$|V_{cb}|$ from inclusive semileptonic B decays

Abstract

We determine $|V_{cb}|$ from inclusive semileptonic B decays including resummation of supposedly large perturbative corrections, which originate from the running of the strong coupling. We argue that the low value of the BLM scale found previously for inclusive decays is a manifestation of the renormalon divergence of the perturbative series starting already in third order. A reliable determination of $|V_{cb}|$ from inclusive decays is still possible if one uses a short-distance b quark mass. We find that using the $\overline{\rm MS}$ running mass significantly reduces the perturbative coefficients already in low orders. For a semileptonic branching ratio of $10.9\%$ we obtain $|V_{cb}|(τ_B/1.50\,{\rm ps})^{1/2}=0.041\pm 0.002\pm 0.002$. This work was done in collaboration with M. Beneke and V.M.\ Braun.