Covariant light-front approach for $$B_c$$ B c decays into charmonium: implications on form factors and branching ratios

Abstract In this work, we investigate the form factors of $$B_c$$ B c decays into $$J/\Psi , \psi (2S,3S),\eta _c,$$ J / Ψ , ψ ( 2 S , 3 S ) , η c , $$ \eta _c(2\,S,3\,S), \chi _{c0}, \chi _{c1}, h_c$$ η c ( 2 S , 3 S ) , χ c 0 , χ c 1 , 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 $$B_c\rightarrow D^{(*)}, D^{(*)}_s$$ B c → D ( ∗ ) , D s ( ∗ ) 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 $$q^2$$ q 2 dependence for each transition form factor is also plotted. Then, using the factorization method, we calculate the branching ratios of 80 $$B_c$$ 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 $$\psi (2S,3S)$$ ψ ( 2 S , 3 S ) and $$\eta _c(2S,3S)$$ η c ( 2 S , 3 S ) , 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.