Observations of the singly Cabibbo-suppressed decays $\hat{I}{ž}_c^{+}\to p{K}_S^0$, $\hat{I}{ž}_c^{+}\to \hat{I}›\ddot{I}{€}^{+}$, and $\hat{I}{ž}_c^{+}\to \hat{I}{\pounds }^0\ddot{I}{€}^{+}$ 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 $\hat{I}{ž}_c^{+}\to p{K}_S^0$, $\hat{I}{ž}_c^{+}\to \hat{I}›\ddot{I}{€}^{+}$, and $\hat{I}{ž}_c^{+}\to \hat{I}{\pounds }^0\ddot{I}{€}^{+}$ are observed for the first time. The ratios of branching fractions of $\hat{I}{ž}_c^{+}\to p{K}_S^0$, $\hat{I}{ž}_c^{+}\to \hat{I}›\ddot{I}{€}^{+}$, and $\hat{I}{ž}_c^{+}\to \hat{I}{\pounds }^0\ddot{I}{€}^{+}$ relative to that of $\hat{I}{ž}_c^{+}\to \hat{I}{ž}^{-}\ddot{I}{€}^{+}\ddot{I}{€}^{+}$ are measured to be \begin{equation} \frac{{\cal B}(Ξ_c^+ \to pK_S^0)}{{\cal B}(Ξ_c^{+} \to Ξ^{-} π^+ π^+)} = (2.47 \pm 0.16 \pm 0.07)\% \notag, \end{equation} \begin{equation} \frac{{\cal B}(Ξ_c^+ \to Λπ^+)}{{\cal B}(Ξ_c^{+} \to Ξ^{-} π^+ π^+)} = (1.56 \pm 0.14 \pm 0.09)\% \notag, \end{equation} \begin{equation} \frac{{\cal B}(Ξ_c^+ \to Σ^0 π^+)}{{\cal B}(Ξ_c^{+} \to Ξ^{-} π^+ π^+)} = (4.13 \pm 0.26 \pm 0.22)\% \notag. \end{equation} Multiplying these values by the branching fraction of the normalization channel, $\mathcal{B}(\hat{I}{ž}_c^{+}\to \hat{I}{ž}^{-}\ddot{I}{€}^{+}\ddot{I}{€}^{+})=(2.9\pm 1.3)\%$, the absolute branching fractions are determined to be \begin{equation} {\cal B}(Ξ_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}(Ξ_c^{+} \to Λπ^+) = (4.52 \pm 0.41 \pm 0.26 \pm 2.03) \times 10^{-4} \notag, \end{equation} \begin{equation} {\cal B}(Ξ_c^{+} \to Σ^0 π^+) = (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 $\mathcal{B}(\hat{I}{ž}_c^{+}\to \hat{I}{ž}^{-}\ddot{I}{€}^{+}\ddot{I}{€}^{+})$.

21 pages, 5 pages