First Observation of the Cabibbo Suppressed Decay ${B^{+}\to {\overline{\mathit{D}}}^0\mathit{K}}^{+}$

We have observed the decay $B^{+}\to {\overline{D}}^0{K}^{+}$, using $3.3\times {10}^6$ $B\overline{B}$ pairs collected with the CLEO II detector at the Cornell Electron Storage Ring. We find the ratio of branching fractions $R\equiv B(B^{+}\to {\overline{D}}^0{K}^{+})/B(B^{+}\to {\overline{D}}^0{\pi }^{+})=0.055\mathrm{}\pm 0.014\pm 0.005$.