Search for CP violation and measurement of branching fractions and decay asymmetry parameters for Λc+→Λh+ and Λc+→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⁺.

Recent Measurements of Decay Asymmetry Parameter and CP Asymmetry for Charmed Baryon Decays at Belle

We review the recent results from the Belle experiment on the measurements of branching fractions and decay asymmetry parameters (α) for the hadronic weak decays of charmed baryons, including Λc+→B+P: Λc+→(Λ,Σ0)h+ (h=π,K) and Λc+→Σ+(π0,η,η′); Ξc0→B+P: Ξc0→Ξ−π+; Ξc0→B+V: Ξc0→ΛK¯*0, Ξc0→Σ0K¯*0, and Ξc0→Σ+K*−. In addition, we present an overview of the searches for CP violation via the α-induced CP asymmetry for Λc+→(Λ,Σ0)h+ and Ξc0→Ξ−π+. Finally, we discuss the promising decay modes of Ωc0 which can be measured in the near future and are indispensable in searching for CP violation in the charm sector.

Recent Progress in Λc+ Decays

Studying Λc+ decays provides important and complementary information to help understand the effects of non-perturbative quantum chromodynamics. Recently, many interesting results about Λc+ decays have been reported thanks to the high luminosity in Belle and dedicated operation at the Λc+ pair production threshold in BESIII. This paper reviews the recent progress in experimental measurements, containing sections about the hadronic weak decay, semileptonic decay, and decay asymmetry parameters and CP violation.

Observation of the Singly Cabibbo Suppressed Decay Λ_{c}^{+}→nπ^{+}

The singly Cabibbo-suppressed decay Λ_{c}^{+}→nπ^{+} is observed for the first time with a statistical significance of 7.3σ by using 3.9  fb^{-1} of e^{+}e^{-} collision data collected at center-of-mass energies between 4.612 and 4.699 GeV with the BESIII detector at BEPCII. The branching fraction of Λ_{c}^{+}→nπ^{+} is measured to be (6.6±1.2_{stat}±0.4_{syst})×10^{-4}. By taking the upper limit of branching fractions of Λ_{c}^{+}→pπ^{0} from the Belle experiment, the ratio of branching fractions between Λ_{c}^{+}→nπ^{+} and Λ_{c}^{+}→pπ^{0} is calculated to be larger than 7.2 at the 90% confidence level, which disagrees with most predictions of the available phenomenological models. In addition, the branching fractions of the Cabibbo-favored decays Λ_{c}^{+}→Λπ^{+} and Λ_{c}^{+}→Σ^{0}π^{+} are measured to be (1.31±0.08_{stat}±0.05_{syst})×10^{-2} and (1.22±0.08_{stat}±0.07_{syst})×10^{-2}, respectively, which are consistent with previous results.