We report the first observation of the Cabibbo-suppressed decays $\Xi_c^0\rightarrow \Xi^- K^+$, $\Xi_c^0\ra\Lambda K^+ K^-$ and $\Xi_c^0\rightarrow \Lambda \phi$, using a data sample of $711\, \mathrm{ fb}^{ -1}$ collected at the $\Upsilon(4S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^+ e^-$ collider. We measure the ratios of branching fractions to be $\frac{ { \cal B}(\Xi_c^0\ra \Xi^- K^+)}{ { \cal B}(\Xi^0_c\ra\Xi^-\pi^+)}=(2.75\pm 0.51\pm 0.25)\times 10^{ -2}$, $\frac{ { \cal B}(\Xi_c^0\ra\Lambda K^+ K^-)}{ { \cal B}(\Xi_c^0\rightarrow\Xi^- \pi^+)}=(2.86\pm 0.61\pm 0.24)\times 10^{ -2}$ and $\frac{ { \cal B}(\Xi_c^0\ra \Lambda\phi)}{ { \cal B}(\Xi^0_c\ra\Xi^-\pi^+)}=(3.43\pm 0.58\pm 0.32)\times 10^{ -2}$, where the first uncertainty is statistical and the second is systematic.
Categories: hep-ex