The B-c meson lifetime in the light-front constituent quark model

We present an investigation of the total decay rate of the (ground state) B -c mason within the framework of the relativistic constituent quark model f ormulated on the light-front (LF). The exclusive semileptonic (SL) and nonl eptonic (NL) beauty and charm decays of the B-c meson are described through vector and axial hadronic form factors, which are calculated in terms of q uark model LF wave functions. The latter ones are derived via the Hamiltoni an LF formalism using as input the update constituent quark models. The inc lusive SL and NL partial rates are calculated within a convolution approach inspired by the partonic model and involving the same B-c wave function wh ich is used for evaluation of the exclusive modes. The framework incorporat es systematically 84 exclusive and 44 inclusive partial rates corresponding to the underlying (b) over bar --> (c) over bar and c --> s quark decays. We find tau(Bc) = 0.59 +/- 0.06 ps where the theoretical uncertainty is dom inated by the uncertainty in the choice of LF wave functions acid the thres hold values for the hadron continuum. For the branching fractions of the B- c(+) --> J/psi mu(+)nu(mu) and B-c(+) --> J/psi pi(+) decays we obtain 1.68 and 0.1%, respectively. (C) 1999 Elsevier Science B.V. All rights reserved .