Model-independent investigation of the RJ/ψ, ηc and ratios of decay widths of semileptonic Bc decays into a P-wave charmonium

Experimental measurements of decay branching fractions of semitaunic and semimuonic B-c into J/psi have challenged the lepton flavor universality in standard models with about two standard deviations. In this paper, we first investigate the unitary constraint on form factors of B-c meson into S-wave and P-wave charmonium. Such constraint leads to the exploration of the R-J/psi and other ratios R-eta c, R-hc, and R-chi cJ in a model-independent way. These results together with future experimental measurements can be used to explore the lepton flavor universality in a more systematic way. In addition, we point out that the helicity-dependent ratios R-J/psi(L), and R-J/psi(perpendicular to) can also provide complementary information.