Exclusive and Inclusive Decays of the B_c Meson in the Light-Front ISGW Model

We investigate the total decay rate of the (ground state) $B_c$ meson within the framework of the relativistic constituent quark model formulated on the light-front (LF). The exclusive semileptonic (SL) and nonleptonic (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 the overlap of the parent and daughter LF wave functions. The latters are derived via the Hamiltonian LF formalism using as input the update version of the ISGW model. The inclusive SL and NL partial rates are calculated within a convolution approach inspired by the partonic model and involving the same $B_c$ wave function which is used for evaluation of the exclusive modes. We predict the partial rates for 74 exclusive SL and NL channels and 43 inclusive partial rates corresponding to the underlying $\bar{b}\to \bar{c}$ and $c\to s$ quark decays. Based on our approach we find $\Gamma^{\bar{b}}(B_c)= 0.52 \pm 0.02 ps^{-1}$, $\Gamma^{c}(B_c)= 0.98 \pm 0.07 ps^{-1}$, where the theoretical uncertainty is dominated by the uncertainty in the choice of the threshold values at which the hadron continuum starts. For the $B_c$ lifetime we obtain $\tau_{B_c}= 0.63 \pm 0.02 ps$ in a good agreement with the prediction obtained using the nonrelativistic operator product expansion. We also predict decay rates for many specific weak transitions of $B_c$. In particular, for the branching fractions of the $B^+_c \to J/\psi\mu^+\nu_{\mu}$, $B_c^+\to J/\psi\pi^+$ and $B_c^+ \to J/\psi+X $ decays we obtain 1.7%, 0.1 % and 13.2%, respectively.