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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. 2023 Nov 10;131(19):191802. doi: 10.1103/PhysRevLett.131.191802.
The quantum entangled J/ψ→Σ^{+}Σ[over ¯]^{-} pairs from (1.0087±0.0044)×10^{10} J/ψ events taken by the BESIII detector are used to study the nonleptonic two-body weak decays Σ^{+}→nπ^{+} and Σ[over ¯]^{-}→n[over ¯]π^{-}. The CP-odd weak decay parameters of the decays Σ^{+}→nπ^{+} (α_{+}) and Σ[over ¯]^{-}→n[over ¯]π^{-} (α[over ¯]{-}) are determined to be 0.0481±0.0031{stat}±0.0019_{syst} and -0.0565±0.0047_{stat}±0.0022_{syst}, respectively. The decay parameter α[over ¯]{-} is measured for the first time, and the accuracy of α{+} is improved by a factor of 4 compared to the previous results. The simultaneously determined decay parameters allow the first precision CP symmetry test for any hyperon decay with a neutron in the final state with the measurement of A_{CP}=(α_{+}+α[over ¯]{-})/(α{+}-α[over ¯]{-})=-0.080±0.052{stat}±0.028_{syst}. Assuming CP conservation, the average decay parameter is determined as ⟨α_{+}⟩=(α_{+}-α[over ¯]{-})/2=-0.0506±0.0026{stat}±0.0019_{syst}, while the ratios α_{+}/α_{0} and α[over ¯]{-}/α[over ¯]{0} are -0.0490±0.0032_{stat}±0.0021_{syst} and -0.0571±0.0053_{stat}±0.0032_{syst}, where α_{0} and α[over ¯]_{0} are the decay parameters of the decays Σ^{+}→pπ^{0} and Σ[over ¯]^{-}→p[over ¯]π^{0}, respectively.
利用北京谱仪III（BESIII）探测器采集的（1.0087±0.0044）×10¹⁰个J/ψ事例中的量子纠缠J/ψ→Σ⁺Σ⁻对，研究非轻子两体弱衰变Σ⁺→nπ⁺和Σ⁻→nπ⁻。确定衰变Σ⁺→nπ⁺（α₊）和Σ⁻→nπ⁻（α₋）的CP奇宇称弱衰变参数分别为0.0481±0.0031统计±0.0019系统和 -0.0565±0.0047统计±0.0022系统。首次测量了衰变参数α₋，与先前结果相比，α₊的精度提高了4倍。同时确定的衰变参数使得能够首次对末态有中子的任何超子衰变进行精确的CP对称性检验，测量的CP不对称性A_CP =(α₊ + α₋)/(α₊ - α₋)= -0.080±0.052统计±0.028系统。假设CP守恒，确定平均衰变参数为⟨α₊⟩=(α₊ - α₋)/2 = -0.0506±0.0026统计±0.0019系统，而α₊/α₀和α₋/α₀的比值分别为 -0.0490±0.0032统计±0.0021系统和 -0.0571±0.0053统计±0.0032系统，其中α₀和α₀分别是衰变Σ⁺→pπ⁰和Σ⁻→pπ⁰的衰变参数。
