Measurements of the branching fractions of Ξ c⁺→ Σ ⁺KS⁰, Ξ c⁺→ Ξ ⁰π ⁺, and Ξ c⁺→ Ξ ⁰K+ at Belle and Belle II

A bstract Using 983.0 fb − 1 and 427.9 fb − 1 data samples collected with the Belle and Belle II detectors at the KEKB and SuperKEKB asymmetric energy e + e − colliders, respectively, we present studies of the Cabibbo-favored Ξ c⁺ decays Ξ c⁺→ Σ ⁺KS⁰ and Ξ c⁺→ Ξ ⁰π ⁺ , and the singly Cabibbo-suppressed decay Ξ c⁺→ Ξ ⁰K⁺ . The ratios of branching fractions of Ξ c⁺→ Σ ⁺KS⁰ and Ξ c⁺→ Ξ ⁰K⁺ relative to that of Ξ c⁺→ Ξ ⁻π ⁺π ⁺ are measured for the first time, while the ratio B(Ξ c⁺→ Ξ ⁰π ⁺)/B(Ξ c⁺→ Ξ ⁻π ⁺π ⁺) is also determined and improved by an order of magnitude in precision. The measured branching fraction ratios are $${array}{c}{B({Ξ }c⁺→ {Σ }⁺{K}S⁰)}{B({Ξ }c⁺→ {Ξ }⁻{π }⁺{π }⁺)}=0.067± 0.007± 0.003,\\ {B({Ξ }c⁺→ {Ξ }⁰{π }⁺)}{B({Ξ }c⁺→ {Ξ }⁻{π }⁺{π }⁺)}=0.251± 0.005± 0.010,\\ {B({Ξ }c⁺→ {Ξ }⁰{K}⁺)}{B({Ξ }c⁺→ {Ξ }⁻{π }⁺{π }⁺)}=0.017± 0.003± 0.001.{array}$$ Additionally, the ratio $$B({Ξ }c⁺→ {Ξ }⁰{K}⁺)/B({Ξ }c⁺→ {Ξ }⁰{π }⁺)$$ is measured to be 0 . 068 ± 0 . 010 ± 0 . 004. Here, the first and second uncertainties are statistical and systematic, respectively. Multiplying the ratios by the branching fraction of the normalization mode, B(Ξ c⁺→ Ξ ⁻π ⁺π ⁺)=(2.9± 1.3)% , we obtain the following absolute branching fractions $${array}{c}B({Ξ }c⁺→ {Σ }⁺{K}S⁰)=(0.194± 0.021± 0.009± 0.087)%,\\ B({Ξ }c⁺→ {Ξ }⁰{π }⁺)=(0.728± 0.014± 0.027± 0.326)%,\\ B({Ξ }c⁺→ {Ξ }⁰{K}⁺)=(0.049± 0.007± 0.003± 0.022)%,{array}$$ where the third uncertainties are from $$B({Ξ }c⁺→ {Ξ }⁻{π }⁺{π }⁺)$$ .