Observations of the singly Cabibbo-suppressed decays ${\Xi }_c^{+}\to p{K}_S^0$, ${\Xi }_c^{+}\to \Lambda {\pi }^{+}$, and ${\Xi }_c^{+}\to {\Sigma }^0{\pi }^{+}$ at Belle and Belle II

Abstract

Using data samples of 983.0~$\mathrm{f}{\mathrm{b}}^{-1}$ and 427.9~$\mathrm{f}{\mathrm{b}}^{-1}$ accumulated with the Belle and Belle~II detectors operating at the KEKB and SuperKEKB asymmetric-energy $e^{+}{e}^{-}$ colliders, singly Cabibbo-suppressed decays ${\Xi }_c^{+}\to p{K}_S^0$, ${\Xi }_c^{+}\to \Lambda {\pi }^{+}$, and ${\Xi }_c^{+}\to {\Sigma }^0{\pi }^{+}$ are observed for the first time. The ratios of branching fractions of ${\Xi }_c^{+}\to p{K}_S^0$, ${\Xi }_c^{+}\to \Lambda {\pi }^{+}$, and ${\Xi }_c^{+}\to {\Sigma }^0{\pi }^{+}$ relative to that of ${\Xi }_c^{+}\to {\Xi }^{-}{\pi }^{+}{\pi }^{+}$ are measured to be \begin{equation} \frac{{\cal B}(\Xi_c^+ \to pK_S^0)}{{\cal B}(\Xi_c^{+} \to \Xi^{-} \pi^+ \pi^+)} = (2.47 \pm 0.16 \pm 0.07)\% \notag, \end{equation} \begin{equation} \frac{{\cal B}(\Xi_c^+ \to \Lambda \pi^+)}{{\cal B}(\Xi_c^{+} \to \Xi^{-} \pi^+ \pi^+)} = (1.56 \pm 0.14 \pm 0.09)\% \notag, \end{equation} \begin{equation} \frac{{\cal B}(\Xi_c^+ \to \Sigma^0 \pi^+)}{{\cal B}(\Xi_c^{+} \to \Xi^{-} \pi^+ \pi^+)} = (4.13 \pm 0.26 \pm 0.22)\% \notag. \end{equation} Multiplying these values by the branching fraction of the normalization channel, $\mathcal{B}({\Xi }_c^{+}\to {\Xi }^{-}{\pi }^{+}{\pi }^{+})=(2.9\pm 1.3)\%$, the absolute branching fractions are determined to be \begin{equation} {\cal B}(\Xi_c^{+} \to p K_{S}^{0}) = (7.16 \pm 0.46 \pm 0.20 \pm 3.21) \times 10^{-4} \notag, \end{equation} \begin{equation} {\cal B}(\Xi_c^{+} \to \Lambda \pi^+) = (4.52 \pm 0.41 \pm 0.26 \pm 2.03) \times 10^{-4} \notag, \end{equation} \begin{equation} {\cal B}(\Xi_c^{+} \to \Sigma^0 \pi^+) = (1.20 \pm 0.08 \pm 0.07 \pm 0.54) \times 10^{-3} \notag. \end{equation} The first and second uncertainties above are statistical and systematic, respectively, while the third ones arise from the uncertainty in $\mathcal{B}({\Xi }_c^{+}\to {\Xi }^{-}{\pi }^{+}{\pi }^{+})$.

Comments: 21 pages, 5 pages