Covariant light-front approach for B${}_c$ decays into charmonium. Implications on form factors and branching ratios

In this work, we investigate the form factors of B${}_c$ decays into J/Ψ, ψ(2S,3S), η${}_c$, η${}_c$(2S, 3S), χ${}_{c0}$, χ${}_{c1}$, h${}_c$, and X(3872) mesons in the covariant light-front quark model (CLFQM). For the purpose of the branching ratio calculation, the form factors of B${}_c$ → D${}^{(\ast )}$, D${}_s^{(\ast )}$ transitions are also included. In order to obtain the form factors for the physical transition processes, we need to extend these form factors from the space-like region to the time-like region. The q${}^2$ dependence for each transition form factor is also plotted. Then, using the factorization method, we calculate the branching ratios of 80 B${}_c$ decay channels with a charmonium involved in each mode. Most of our predictions are comparable to the results given by other approaches. As to the decays with the radially excited-state S-wave charmonia involved, such as ψ(2S, 3S) and η${}_c$(2S, 3S), two sets of parameters for their light-front wave functions, corresponding to scenario I (SI) and scenario II (SII), are adopted to calculate the branching ratios. By comparing with the future experimental data, one can discriminate which parameters are more favored.