Using proton-proton collision data corresponding to an integrated luminosity of 3.0 fb$^{ -1}$, recorded by the LHCb detector at centre-of-mass energies of 7 and 8 TeV, the $B_{ c}^{ +} \rightarrow D^{ 0} K^{ +}$ decay is observed with a statistical significance of 5.1 standard deviations. By normalising to $B^{ +} \rightarrow \bar{ D}^{ 0} \pi^{ +}$ decays, a measurement of the branching fraction multiplied by the production rates for $B_{ c}^{ +}$ relative to $B^{ +}$ mesons in the LHCb acceptance is obtained, $$ R_{ D^{ 0} K} = \frac{ f_{ c}}{ f_{ u}}\times\mathcal{ B}(B_{ c}^{ +} \rightarrow D^{ 0} K^{ +}) = (9.3\,^{ +2.8}_{ -2.5} \pm 0.6) \times 10^{ -7}\,, $$ where the first uncertainty is statistical and the second is systematic. This decay is expected to proceed predominantly through weak annihilation and penguin amplitudes, and is the first $B_{ c}^{ +}$ decay of this nature to be observed.
Categories: hep-ex