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

In the wake of the recent measurements of the decays $B_c\to J\mathrm{/}\psi \pi (K)$ and $B_c\to J\mathrm{/}\psi \mathrm{\ell }{\nu }_{\mathrm{\ell }}$ reported by the LHCb Collaboration we calculate the form factors for the $B_c\to J\mathrm{/}\psi$ 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}}_{{\mathcal{\pi }}^{+}\mathcal{/}{\mathcal{\mu }}^{+}\mathcal{\nu }}$$ are in good agreement with last LHCb-data. However, the prediction for the ${\mathcal{R}}_{J\mathrm{/}\psi }$ is found to be underestimated.