A QCD TREATMENT OF THE WEAK DECAYS OF HEAVY FLAVOUR HADRONS -- WITHOUT VOODOO AND UNDUE INCANTATIONS

Abstract

There now exist several theoretical technologies for treating weak decays of heavy flavour hadrons that are genuinely based on QCD without having to invoke a deus ex machina. I focus on one of those, which employs an expansion in inverse powers of the heavy quark mass. It has developed into a rather mature framework incorporating many subtle aspects of quantum field theory. I describe its methodology for treating fully integrated decay rates as well as differential distributions, in particular energy spectra; the importance of a new type of sum rules, the SV sum rules, is emphasized. First practical benefits from this theoretical technology are listed, like predictions on lifetime ratios and extracting the KM parameter $|V(cb)|$ from inclusive and from exclusive semileptonic $B$ decays. An outlook is given onto future developments concerning the determination of the properly defined mass of the heavy quark and its kinetic energy and a reliable extraction of $|V(ub)/V(cb)|$. A few comments on charm decays are added.