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Abstract

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.