Observation ofB±→ωK±Decay

We report the first observation of the charmless two-body mode $B^{\pm }\to \omega K^{\pm }$ decay, and a new measurement of the branching fraction for the $B^{\pm }\to \omega {\pi }^{\pm }$ decay. The measured branching fractions are $\mathcal{B}(B^{\pm }\to \omega K^{\pm })=({9.2}_{-2.3}^{+2.6}\pm 1.0)\times {10}^{-6}$ and $\mathcal{B}(B^{\pm }\to \omega {\pi }^{\pm })=({4.2}_{-1.8}^{+2.0}\pm 0.5)\times {10}^{-6}$. We also measure the partial rate asymmetry of $B^{\pm }\to \omega K^{\pm }$ decays and obtain ${\mathcal{A}}_{CP}=-0.21\pm 0.28\pm 0.03$. The results are based on a data sample of $29.4{\mathrm{f}\mathrm{b}}^{-1}$ collected on the ${\rm Y}(4S)$ resonance by the Belle detector at the KEKB $e^{+}{e}^{-}$ collider.