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Institute of High Energy Physics, Beijing 100049, People's Republic of China.
G.I. Budker Institute of Nuclear Physics SB RAS (BINP), Novosibirsk 630090, Russia.
Phys Rev Lett. 2022 Sep 23;129(13):131801. doi: 10.1103/PhysRevLett.129.131801.
Based on 10 billion J/ψ events collected at the BESIII experiment, a search for CP violation in Λ decay is performed in the difference between CP-odd decay parameters α_{-} for Λ→pπ^{-} and α_{+} for Λ[over ¯]→p[over ¯]π^{+} by using the process e^{+}e^{-}→J/ψ→ΛΛ[over ¯]. With a five-dimensional fit to the full angular distributions of the daughter baryon, the most precise values for the decay parameters are determined to be α_{-}=0.7519±0.0036±0.0024 and α_{+}=-0.7559±0.0036±0.0030, respectively. The Λ and Λ[over ¯] averaged value of the decay parameter is extracted to be α_{avg}=0.7542±0.0010±0.0024 with unprecedented accuracy. The CP asymmetry A_{CP}=(α_{-}+α_{+})/(α_{-}-α_{+}) is determined to be -0.0025±0.0046±0.0012, which is one of the most precise measurements in the baryon sector. The reported results for the decay parameter will play an important role in the studies of the polarizations and CP violations for the strange, charmed and beauty baryons.
基于在BESIII实验中收集的100亿个J/ψ事例，通过过程e⁺e⁻→J/ψ→ΛΛ̅，在Λ→pπ⁻的CP奇宇称衰变参数α₋与Λ̅→p̅π⁺的α₊之间的差异中进行Λ衰变中CP破坏的搜寻。通过对末态重子的全角分布进行五维拟合，确定衰变参数的最精确值分别为α₋ = 0.7519±0.0036±0.0024和α₊ = -0.7559±0.0036±0.0030。提取出Λ和Λ̅衰变参数的平均值为α_avg = 0.7542±0.0010±0.0024，精度达到前所未有的水平。CP不对称性A_CP = (α₋ + α₊)/(α₋ - α₊)被确定为-0.0025±0.0046±0.0012，这是重子领域最精确的测量结果之一。所报道的衰变参数结果将在奇异、粲和底重子的极化及CP破坏研究中发挥重要作用。
