We report the first observation of the Cabibbo-suppressed decays ${\Xi }_c^0\to {\Xi }^{-}{K}^{+}$, ${\Xi }_c^0\to \Lambda K^{+}{K}^{-}$ and ${\Xi }_c^0\to \Lambda \varphi$, using a data sample of $711{\mathrm{fb}}^{-1}$ collected at the ${\rm Y}(4S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^{+}{e}^{-}$ collider. We measure the ratios of branching fractions to be $\frac{\mathcal{B}({\Xi }_c^0\to {\Xi }^{-}{K}^{+})}{\mathcal{B}({\Xi }_c^0\to {\Xi }^{-}{\pi }^{+})}=(2.75\pm 0.51\pm 0.25)\times {10}^{-2}$, $\frac{\mathcal{B}({\Xi }_c^0\to \Lambda K^{+}{K}^{-})}{\mathcal{B}({\Xi }_c^0\to {\Xi }^{-}{\pi }^{+})}=(2.86\pm 0.61\pm 0.37)\times {10}^{-2}$ and $\frac{\mathcal{B}({\Xi }_c^0\to \Lambda \varphi )}{\mathcal{B}({\Xi }_c^0\to {\Xi }^{-}{\pi }^{+})}=(3.43\pm 0.58\pm 0.32)\times {10}^{-2}$, where the first uncertainty is statistical and the second is systematic.

• Received 25 June 2013

DOI:https://doi.org/10.1103/PhysRevD.88.071103