Exclusive and inclusive decays of the B-c meson in the light-front ISGW model

We investigate the total decay width of the (ground-state) B-c meson within the relativistic constituent quark model formulated on the light front (LF ). The exclusive semileptonic (SL) and nonleptonic (NL) beauty and charm de cays of the B-c meson are described with the aid of the vector and axial ha dronic form factors, which are calculated in terms of the overlap of the co nstituent-quark-model LF wave functions. The latter are derived via the Ham iltonian LF formalism by using the updated version of the ISGW model as an input. The inclusive SL and NL partial rates are calculated within a convol ution approach that is inspired by the partonic model and which involves th e same B-c wave function as that which is used to evaluate exclusive modes. We predict the partial rates for 84 exclusive and 44 inclusive partial rat es corresponding to the underlying (b) over bar --> (c) over bar and c --> s quark decays. On the basis of our approach. we obtain r((b) over bar)(B-c ) = 0.52 +/- 0.02 ps(-1) and Gamma(c)(B-c)= 0.98 +/- 0.07 ps(-1), where the theoretical uncertainties are dominated by the uncertainty in the choice o f the threshold of the hadron continuum. For the B-c lifetime, we arrive at tau(Bc) = 0.63 +/- 0.02 ps, in good agreement with the prediction obtained by using a nonrelativistic operator-product expansion. We also predict dec ay rates for many specific weak transitions of B-c. In particular, we obtai n 1.7%, 0.1%, and 13.2% for the B-c(+) --> J/psi mu(+)v(mu), B-c(+) --> J/p si mu(+), and Bc(+) --> J/psi + X branching fractions, respectively.