Observation of $D_s^{+}$→K${¯}^0$$K^{+}$ and $D_s^{+}$→K${¯}^0$$K^{+}$ and an upper limit on $D_s^{+}$→$K^0$${\pi }^{+}$

We report the first observation of the decay ${\mathit{D}}_{\mathit{s}}^{+}$→K¯ ${}_{}{}^0{}_{}{}^{}$ ${\mathit{K}}^{+}$ and a new measurement of the decay ${\mathit{D}}_{\mathit{s}}^{+}$→K¯ (892${)}^0$ ${\mathit{K}}^{+}$. The data were collected at √s=4.14 GeV with the Mark III detector at the SLAC ${\mathit{e}}^{+}$ ${\mathit{e}}^{\mathrm{-}}$ storage ring at SPEAR. We obtain the relative branching fractions B(${\mathit{D}}^{+}$s→K${\mathrm{¯}}^0$ ${\mathit{K}}^{+}$/ B(${\mathit{D}}_{\mathit{s}}^{+}$→φ${\mathrm{\pi }}^{+}$)=0.92±0.32±0.20 and B(${\mathit{D}}_{\mathit{s}}^{+}$→K${\mathrm{¯}}^{\mathrm{*}0}$ ${\mathit{K}}^{+}$)/ B(${\mathit{D}}_{\mathit{s}}^{+}$→φ${\mathrm{\pi }}^{+}$)=0.84±0.30±0.22, using our new determination of σB(${\mathit{D}}_{\mathit{s}}^{+}$→φ${\mathrm{\pi }}^{+}$). A search for the Cabibbo-suppressed decay ${\mathit{D}}^{+}$s→${\mathit{K}}^0$ ${\mathrm{\pi }}^{+}$ yields a limit B(${\mathit{D}}_{\mathit{s}}^{+}$→${\mathit{K}}^0$ ${\mathrm{\pi }}^{+}$)/B(${\mathit{D}}_{\mathit{s}}^{+}$→φ${\mathrm{\pi }}^{+}$)<0.21 at the 90% confidence level.