Search for CP violation and measurement of branching fractions and decay asymmetry parameters for Λ_c⁺→Λh⁺ and Λ_c⁺→Σ⁰h⁺ (h=K,π)

We report a study of Λ_c⁺→Λh⁺ and Λ_c⁺→Σ⁰h⁺ (h=K,π) decays based on a data sample of 980fb^-1 collected with the Belle detector at the KEKB energy-asymmetric e⁺e^- collider. The first results of direct CP asymmetry in two-body singly Cabibbo-suppressed (SCS) decays of charmed baryons are measured, A_CP^dir(Λ_c⁺→ΛK⁺)=+0.021±0.026±0.001 and A_CP^dir(Λ_c⁺→Σ⁰K⁺)=+0.025±0.054±0.004. We also make the most precise measurement of the decay asymmetry parameters (α) for the four modes of interest and search for CP violation via the α-induced CP asymmetry (A_CP^α). We measure A_CP^α(Λ_c⁺→ΛK⁺)=-0.023±0.086±0.071 and A_CP^α(Λ_c⁺→Σ⁰K⁺)=+0.08±0.35±0.14, which are the first A_CP^α results for SCS decays of charmed baryons. We search for Λ-hyperon CP violation in Λ_c⁺→(Λ,Σ⁰)π⁺ and find A_CP^α(Λ→pπ^-)=+0.013±0.007±0.011. This is the first time that hyperon CP violation has been measured via Cabibbo-favored charm decays. No evidence of baryon CP violation is found. We also obtain the most precise branching fractions for two SCS Λ_c⁺ decays, B(Λ_c⁺→ΛK⁺)=(6.57±0.17±0.11±0.35)×10^-4 and B(Λ_c⁺→Σ⁰K⁺)=(3.58±0.19±0.06±0.19)×10^-4. The first uncertainties are statistical and the second systematic, while the third uncertainties come from the uncertainties on the world average branching fractions of Λ_c⁺→(Λ,Σ⁰)π⁺.