Semileptonic Bc → ηc,J/ψ transitions

Abstract

Using a systematic, symmetry-preserving continuum approach to the Standard Model strong-interaction bound-state problem, we deliver parameter-free predictions for all semileptonic Bc→ηc,J/ψ 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 τ over μ final states are obtained: Rηc=0.313(22) and RJ/ψ=0.242(47). Combined with other recent results, our analysis confirms a 2σ discrepancy between the Standard Model prediction for RJ/ψ and the single available experimental result.