Lawrence Berkeley National Laboratory

The ratio of branching fractions RK/π≡ℬBc+→J/ψK+/ℬBc+→J/ψπ+$$ {R}_{K/\uppi}\equiv \mathrm{\mathcal{B}}\left({\mathrm{B}}_{\mathrm{c}}^{+}\to \mathrm{J}/{\uppsi \mathrm{K}}^{+}\right)/\mathrm{\mathcal{B}}\left({\mathrm{B}}_{\mathrm{c}}^{+}\to \mathrm{J}/{\uppsi \uppi}^{+}\right) $$ is measured with pp collision data collected by the LHCb experiment at centre-of-mass energies of 7 TeV and 8 TeV, corresponding to an integrated luminosity of 3 fb−1. It is found to be RK/π = 0.079 ± 0.007 ± 0.003, where the first uncertainty is statistical and the second is systematic. This measurement is consistent with the previous LHCb result, while the uncertainties are significantly reduced.