Observations of the singly Cabibbo-suppressed decays Ξc+→pKS0, Ξc+→Λπ+, and Ξc+→Σ0π+ at Belle and Belle II

Abstract

Using data samples of 983.0 fb⁻¹ and 427.9 fb⁻¹ accumulated with the Belle and Belle II detectors operating at the KEKB and SuperKEKB asymmetric-energy e⁺e⁻ colliders, singly Cabibbo-suppressed decays ${\mathrm{\Xi }}_c^{+}\to p{K}_S^0$, ${\mathrm{\Xi }}_c^{+}\to \mathrm{\Lambda }{\pi }^{+}$, and ${\mathrm{\Xi }}_c^{+}\to {\mathrm{\Sigma }}^0{\pi }^{+}$ are observed for the first time. The ratios of branching fractions of ${\mathrm{\Xi }}_c^{+}\to p{K}_S^0$, ${\mathrm{\Xi }}_c^{+}\to \mathrm{\Lambda }{\pi }^{+}$, and ${\mathrm{\Xi }}_c^{+}\to {\mathrm{\Sigma }}^0{\pi }^{+}$ relative to that of ${\mathrm{\Xi }}_c^{+}\to {\mathrm{\Xi }}^{-}{\pi }^{+}{\pi }^{+}$ are measured to be$$\begin{array}{c}\frac{\mathcal{B}\left({\mathrm{\Xi }}_c^{+}\to p{K}_S^0\right)}{\mathcal{B}\left({\mathrm{\Xi }}_c^{+}\to {\mathrm{\Xi }}^{-}{\pi }^{+}{\pi }^{+}\right)}=\left(2.47\pm 0.16\pm 0.07\right)\%,\\ \frac{\mathcal{B}\left({\mathrm{\Xi }}_c^{+}\to \mathrm{\Lambda }{\pi }^{+}\right)}{\mathcal{B}\left({\mathrm{\Xi }}_c^{+}\to {\mathrm{\Xi }}^{-}{\pi }^{+}{\pi }^{+}\right)}=\left(1.56\pm 0.14\pm 0.09\right)\%,\\ \frac{\mathcal{B}\left({\mathrm{\Xi }}_c^{+}\to {\mathrm{\Sigma }}^0{\pi }^{+}\right)}{\mathcal{B}\left({\mathrm{\Xi }}_c^{+}\to {\mathrm{\Xi }}^{-}{\pi }^{+}{\pi }^{+}\right)}=\left(4.13\pm 0.26\pm 0.22\right)\%.\end{array}$$

Multiplying these values by the branching fraction of the normalization channel, $\mathcal{B}\left({\mathrm{\Xi }}_c^{+}\to {\mathrm{\Xi }}^{-}{\pi }^{+}{\pi }^{+}\right)=\left(2.9\pm 1.3\right)\%$, the absolute branching fractions are determined to be$$\begin{array}{c}\mathcal{B}\left({\mathrm{\Xi }}_c^{+}\to p{K}_S^0\right)=\left(7.16\pm 0.46\pm 0.20\pm 3.21\right)\times {10}^{-4},\\ \mathcal{B}\left({\mathrm{\Xi }}_c^{+}\to \mathrm{\Lambda }{\pi }^{+}\right)=\left(4.52\pm 0.41\pm 0.26\pm 2.03\right)\times {10}^{-4},\\ \mathcal{B}\left({\mathrm{\Xi }}_c^{+}\to {\mathrm{\Sigma }}^0{\pi }^{+}\right)=\left(1.20\pm 0.08\pm 0.07\pm 0.54\right)\times {10}^{-3}.\end{array}$$

The first and second uncertainties above are statistical and systematic, respectively, while the third ones arise from the uncertainty in $\mathcal{B}\left({\mathrm{\Xi }}_c^{+}\to {\mathrm{\Xi }}^{-}{\pi }^{+}{\pi }^{+}\right)$.