A search for the decays $B_c^+ \to J/\psi D^{ (*)0} K^+$ and $B_c^+ \to J/\psi D^{ (*)+} K^{ *0}$ is performed with data collected at the LHCb experiment corresponding to an integrated luminosity of 3 fb$^{ -1}$. The decays $B_c^+ \to J/\psi D^0 K^+$ and $B_c^+ \to J/\psi D^{ *0} K^+$ are observed for the first time, while first evidence is reported for the $B_c^+ \to J/\psi D^{ *+} K^{ *0}$ and $B_c^+ \to J/\psi D^+ K^{ *0}$ decays. The branching fractions of these decays are determined relative to the $B_c^+ \to J/\psi \pi^+$ decay. The $B_c^+$ mass is measured, using the $J/\psi D^0 K^+$ final state, to be $6274.28 \pm 1.40 (stat) \pm 0.32 (syst)$ MeV/$c^2$. This is the most precise single measurement of the $B_c^+$ mass to date.
Categories: hep-ex