Semileptonic decays of $B_c$ mesons into charmonium states

In this work we study the semileptonic decays of $B_c$ meson. We evaluated $B_c\to D(D^{\ast })$, $B_c\to D_s(D_s^{\ast })$ and $B_c\to {\eta }_c(J\mathrm{/}\psi )$ transitions form factors in the full kinematical region within the covariant quark model. The calculated form factors are used to evaluate the semileptonic decays of $B_c$ meson and it was defined ratios ($R_{{\eta }_c}$, $R_{J\mathrm{/}\psi }$, $R_D$ ,$R_{D^{\ast }}$) of the branching ratios, which will be hopefully tested on LHC experiments.We compare the obtained results with the results from other theoretical approaches.