Sci Bull (Beijing). 2023 Mar 30;68(6):583-592. doi: 10.1016/j.scib.2023.02.017. Epub 2023 Feb 21.
We report a study of Λ→Λh and Λ→Σh (h=K,π) decays based on a data sample of 980fb collected with the Belle detector at the KEKB energy-asymmetric ee collider. The first results of direct CP asymmetry in two-body singly Cabibbo-suppressed (SCS) decays of charmed baryons are measured, A(Λ→ΛK)=+0.021±0.026±0.001 and A(Λ→ΣK)=+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). We measure A(Λ→ΛK)=-0.023±0.086±0.071 and A(Λ→ΣK)=+0.08±0.35±0.14, which are the first A results for SCS decays of charmed baryons. We search for Λ-hyperon CP violation in Λ→(Λ,Σ)π and find A(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 decays, B(Λ→ΛK)=(6.57±0.17±0.11±0.35)×10 and B(Λ→ΣK)=(3.58±0.19±0.06±0.19)×10. 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→(Λ,Σ)π.
我们报道了一项基于 Belle 探测器在 KEKB 能量非对称 ee 对撞机上采集的 980fb 数据样本对 Λ→Λh 和 Λ→Σh（h=K，π）衰变的研究。首次测量了双Cabibbo 压低（SCS）衰变的 charmed 重子的两体直接 CP 不对称性，A(Λ→ΛK)=+0.021±0.026±0.001 和 A(Λ→ΣK)=+0.025±0.054±0.004。我们还对四个感兴趣模式的衰变不对称参数（α）进行了最精确的测量，并通过 α 诱导的 CP 不对称性（A）搜索 CP 破坏。我们测量到 A(Λ→ΛK)=-0.023±0.086±0.071 和 A(Λ→ΣK)=+0.08±0.35±0.14，这是首次对 charmed 重子 SCS 衰变进行的 A 测量结果。我们在 Λ→(Λ,Σ)π 中搜索 Λ 超子 CP 破坏，并发现 A(Λ→pπ)=+0.013±0.007±0.011。这是首次通过 Cabibbo 有利的 charm 衰变测量到超子 CP 破坏。没有发现重子 CP 破坏的证据。我们还获得了两个 SCS Λ 衰变的最精确分支比，B(Λ→ΛK)=(6.57±0.17±0.11±0.35)×10 和 B(Λ→ΣK)=(3.58±0.19±0.06±0.19)×10。第一个不确定度是统计的，第二个是系统的，第三个不确定度来自于 Λ→(Λ,Σ)π 的世界平均分支比的不确定度。
