Observation of the $W$-Annihilation Decay $D_s^{+}\to \omega {\pi }^{+}$ and Evidence for $D_s^{+}\to \omega K^{+}$

We report on the observation of the $W$-annihilation decay $D^{+}{s} \rightarrow \omega \pi^{+}$andtheevidencefor$D{s}^{+} \rightarrow \omega K^{+}$ with a data sample corresponding to an integrated luminosity of 3.19 fb${}^{-1}$ collected with the BESIII detector at the center-of-mass energy $\sqrt{s}=4.178$ GeV. We obtain the branching fractions $$\mathcal{B}$(D^{+}{s} \rightarrow \omega \pi^{+}) = (1.77\pm0.32{{\rm stat.}}\pm0.11_{{\rm sys.}}) \times 10^{-3}$and$$\mathcal{B}$(D^{+}{s} \rightarrow \omega K^{+}) = (0.87\pm0.24{{\rm stat.}}\pm0.07_{{\rm sys.}}) \times 10^{-3}$, respectively.