The decays $B_c\to J/\psi +\bar{\ell }{\nu }_{\ell }$ and $B_c\to J/\psi +\pi (K)$ in covariant confined quark model

Abstract

In the wake of the recent measurements of the decays $B_c\to J/\psi \pi (K)$ and $B_c\to J/\psi \ell {\nu }_{\ell }$ reported by the LHCb Collaboration we calculate the form factors for the $B_c\to J/\psi$ and $B_c\to {\eta }_c$ transitions in full kinematical region within covariant confined quark model. Then we use the calculated form factors to evaluate the partial decay widths of the above-mentioned semileptonic and nonleptonic decays of the $B_c$ meson. We find that the theoretical predictions on the ratios of ${\mathcal{R}}_{K^{+}/{\pi }^{+}}$ and ${\mathcal{R}}_{{\pi }^{+}/{\mu }^{+}\nu }$ are in good agreement with last LHCb-data. However, the prediction for the ${\mathcal{R}}_{J/\psi }$ is found to be underestimated.