In this work, we investigate the semileptonic decays of $B_{ c}$ meson to $\eta_{ c}(1S,2S,3S)$, $\psi(1S,2S,3S)$ and $X(3872)$ within the framework of covariant light-front quark model (CLFQM). We combine the helicity amplitudes via the corresponding form factors to obtain the branching ratios of the semileptonic decays $B_{ c}\to \eta_{ c}(1S, 2S, 3S)\ell\nu_{ \ell}$, $B_{ c}\to \psi(1S, 2S, 3S))\ell\nu_{ \ell}$ and $B_{ c}\to X(3872)\ell\nu_{ \ell}$ with $\ell=e,\mu,\tau$. In view of the $R_{ J/\Psi}$ anomaly released by the LHCb collaboration, it is necessary to calculate the ratios $R_X$ with $X=\psi(1S,2S,3S),\eta_c(1S,2S,3S),X(3872)$ systematically, which are helpful to check the lepton flavor universality (LFU). Furthermore, we also take into account another two physical observables, one is the longitudinal polarization fraction $f_{ L}$ and the other is the forward-backward asymmetry $A_{ FB}$, which can provide new clues to understand the $R_{ J /\Psi}$ anomaly. Such theoretical predictions are necessary and interesting, which can be tested in the future LHCb experiments.
Categories: hep-ph hep-ex