Measurement of the ratio of $B_c^+$ branching fractions to $J/\psi\pi^+$   and $J/\psi\mu^+\nu_\mu$
  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, ${\cal B}(B_c^+ \to J/\psi \pi^+)/{\cal B}(B_c^+\to J/\psi\mu^+\nu_\mu)=0.0469 \pm 0.0028 (stat.) \pm 0.0046 (syst.)$, is at the lower end of available theoretical predictions. 
LHCb collaboration: R. Aaij, B. Adeva, M. Adinolfi, A. Affolder, Z.   Ajaltouni, S. Akar, J. Albrecht, F. Alessio, M. Alexan...
hep-ex