Recent Advances in Semileptonic B Decays

Abstract

Aspects of the OPE-based QCD theory of B decays are discussed. We have at least one nontrivial precision check of the OPE at the nonperturbative level in inclusive decays. The data suggest proximity to the `BPS' limit for B mesons. Its consequences are addressed and their accuracy qualified. It is suggested that theory-wise B->D \ell\nu near zero recoil offers an accurate alternative way to measure |V_{cb}|. It is shown that the OPE is in a good standing when confronted by experiment. The alleged controversy between theory and data on certain decay channels is found to be an artefact of oversimplifying the OPE in presence of high experimental cuts severely degrading the effective hardness. The effects exponential in the latter are missed in the traditionally used expressions, yet they do not signify a breakdown of the 1/m_b expansion proper. They typically increase the apparent b quark mass in B->X_s+\gamma by 70 MeV or more, together with an even more dramatic downward shift in the kinetic expectation value. The utility of the second moment of E_\gamma is emphasized once the aforementioned effects have been included. Incorporating them brings different measurements into a good agreement, provided the OPE-based theory employs the robust approach.