Measurement of the ratio of $B_c^+$ branching fractions to $J/psipi^+$ and $J/psimu^+ u_mu$

The first measurement that relates semileptonic and hadronic decay rates of the $B_c^+$ meson is performed using proton-proton collision data corresponding to 1.0 fb$^{-1}$ of integrated luminosity collected with the LHCb detector. The measured value of the ratio of branching fractions, ${cal B}(B_c^+ to J/psi pi^+)/{cal B}(B_c^+to J/psimu^+ u_mu)=0.0469 pm 0.0028 (stat.) pm 0.0046 (syst.)$, is at the lower end of available theoretical predictions.