Observation ofB+→ψ(3770)K+

We report the first observation of the decay $B^{+}\to \psi (3770)K^{+}$ where the $\psi (3770)$ is reconstructed in the $D^0{\overline{D}}^0$ and $D^{+}{D}^{-}$ decay channels. The obtained branching fraction is $\mathcal{B}\mathbf{(}{B}^{+}\to \psi (3770)K^{+}\mathbf{)}=(0.48\pm 0.11\pm 0.07)\times {10}^{-3}$. We have measured the branching fraction for the decay $B^{+}\to D^0{\overline{D}}^0{K}^{+}$ to be $(1.17\pm 0.21\pm 0.15)\times {10}^{-3}$ and set a $90\%$ confidence level upper limit of $0.90\times {10}^{-3}$ for the decay $B^{+}\to D^{+}{D}^{-}{K}^{+}$. We also present the results of a search for possible decays to $D\overline{D}$ and $D^0{\overline{D}}^0{\pi }^0$ of the recently observed $X(3872)$ particle. The analysis is based on $88{\mathrm{f}\mathrm{b}}^{-1}$ of data collected at the ${\rm Y}(4S)$ resonance by the Belle detector at the KEKB asymmetric-energy $e^{+}{e}^{-}$ collider.