Semileptonic Bc → ηc, J/ψ transitions

Using a systematic, symmetry-preserving continuum approach to the Standard Model strong-interaction bound-state problem, we deliver parameter-free predictions for all semileptonic B-c -> eta(c), J/psi transition form factors on the complete domains of empirically accessible momentum transfers. Working with branching fractions calculated therefrom, the following values of the ratios for tau over mu final states are obtained: R-eta c = 0.313(22) and R-J/psi = 0.242(47). Combined with other recent results, our analysis confirms a 2 sigma discrepancy between the Standard Model prediction for R-J/psi and the single available experimental result. (C) 2021 The Author(s). Published by Elsevier B.V.

Automated summary

Using a systematic, symmetry-preserving continuum approach, parameter-free predictions were made for all semileptonic B-c -> eta(c), J/psi transition form factors. The study confirms a 2 sigma discrepancy between the Standard Model prediction for R-J/psi and the single available experimental result.