EXCLUSIVE AND INCLUSIVE WEAK DECAYS OF THE B-MESON

A relativistic quark model is applied to the description of semilepton ic and non-leptonic charmed decays of the B-meson. The exclusive semil eptonic modes B --> Dl nu(l) and B --> Dl nu(l) are described through the universal Isgur-Wise form factor, which is calculated in terms of a constituent quark model wave function for the B-meson. Different ap proximations for the latter, either based on a phenomenological ansatz or derived from analyses of the meson spectra, are adopted, In partic ular, two wave functions, constructed via the Hamiltonian light-front formalism using a relativized and a non-relativistic constituent quark model, are considered, obtaining a link between standard spectroscopi c quark models and the B-meson decay physics, The inclusive semilepton ic and non-leptonic branching ratios are calculated within a convoluti on approach, inspired by the partonic model and involving the same B-m eson wave function used for the evaluation of the exclusive semilepton ic modes. Our results for the major branching ratios are consistent wi th available experimental data and the sum of all the calculated branc hing ratios turns out to be close to unity, In particular, we found th at (i) a remarkable fraction (similar to 35%) of semileptonic decay mo des occur in non-D, non-D final states; (ii) non-perturbative effects enhance the inclusive b --> c (u) over bar d decay channels, with a s izable contribution provided by internal decays into heavy mesons and baryon-antibaryon pairs; the resulting reduction of the semileptonic b ranching ratio brings the theoretical prediction in agreement with the experimental value without increasing at the same time the charm coun ting. (C) 1997 Elsevier Science B.V.