Search for $CP$ violation in Ξc⁺→Σ⁺h⁺h⁻ and Λc⁺→ ph⁺h⁻ at Belle II

We report decay-rate $CP$ asymmetries of the singly-Cabibbo-suppressed decays Ξc⁺→Σ⁺h⁺h⁻ and Λc⁺→ ph⁺h⁻, with $h=K,π$, measured using 428 fb⁻¹ of e⁺e⁻ collisions collected by the Belle II experiment at the SuperKEKB collider. The results, {equation} ACP(Ξ_c^+→Σ^+K^+K^-) = (3.7±6.6±0.6)%, {equation}{equation} ACP(Ξ_c^+→Σ^+π^+π^-) = (9.5±6.8±0.5)%, {equation}{equation} ACP(Λ_c^+→ pK^+K^-) = (3.9±1.7±0.7)%, {equation}{equation} ACP(Λ_c^+→ pπ^+π^-) = (0.3±1.0±0.2)%, {equation} where the first uncertainties are statistical and the second systematic, agree with $CP$ symmetry. From these results we derive the sums {equation} ACP(Ξ_c^+→Σ^+π^+π^-) \, + \, ACP(Λ_c^+→ pK^+K^-) = (13.4 ± 7.0± 0.9)%, {equation}{equation} ACP(Ξ_c^+→Σ^+K^+K^-) \, + \, ACP(Λ_c^+→ pπ^+π^-) = ({0}4.0 ± 6.6± 0.7)%, {equation} which are consistent with the U-spin symmetry prediction of zero. These are the first measurements of $CP$ asymmetries for individual hadronic three-body charmed-baryon decays.