Semileptonic Decays of D and B Mesons, Part Ii Iv. B-meson Semileptonic Decays the Inclusive Semileptonic Branching Fraction

In the following sections, we discuss some of the key questions related to semileptonic decays of B mesons: the inclusive semileptonic branching fraction, the determination of jV cb j and jV ub j from inclusive and exclusive measurements, recent progress in exclusive semileptonic decays, and form factor measurements and tests of heavy-quark eeective theory. We emphasize the uncertainties that arise in extracting jV cb j and jV ub j from data. Further discussions of these and related issues are given in the references 1,2,3]. The b-hadron inclusive semileptonic branching fraction, B SL , has been measured both at the (4S), where the b hadrons are a mixture of B + and B 0 mesons, and at the Z, where B s mesons and b baryons are produced as well. Here B SL is the branching fraction to either electrons or muons, not their sum. Semileptonic decays to leptons are suppressed by phase space and have been observed, within large errors, at the expected level 4,5]. Measurements of B SL are given in Table 1 for single-lepton measurements at the (4S), in Table 2 for the LEP experiments, and in Table 3 for dilepton measurements at the (4S).