Measurement of the ratio of branching fractions $\mathcal{B}(B_{c}^{+}   \to J/\psi K^{+})/\mathcal{B}(B_{c}^{+} \to J/\psi\pi^{+})$
  The ratio of branching fractions $R_{K/\pi} \equiv \mathcal{B}(B_{c}^{+} \to J/\psi K^{+})/\mathcal{B}(B_{c}^{+} \to J/\psi\pi^{+})$ 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${\mbox{fb}^{-1}}$. It is found to be $ R_{K/\pi} = 0.079\pm0.007\pm0.003$, 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. 
LHCb collaboration: R. Aaij, B. Adeva, M. Adinolfi, Z. Ajaltouni, S.   Akar, J. Albrecht, F. Alessio, M. Alexander, S. Ali, ...
hep-ex