近日，中国科学院大学物理科学学院傅金林长聘副教授团队依托北京谱仪III（BESIII）实验，首次利用量子纠缠的Λ-反Λ超子体系，实现了迄今最精确的Λ超子电偶极矩（Electric Dipole Moment，EDM）测量。测量精度达到10–19e·cm量级，较1981年美国费米实验室测量结果提高约三个数量级。相关成果以“Measurement of the Λ Electric Dipole Moment with an Entangled Baryon-Antibaryon System”为题发表于《科学》（Science）[1]。

Recently, a team led by Fu Jinlin, a tenured associate professor at the School of Physical Sciences, University of Chinese Academy of Sciences (UCAS), achieved the most precise measurement of the Λ hyperon electric dipole moment (EDM) at the Beijing Spectrometer (BESIII) experiment by using quantum-entangled Λ–anti-Λ pairs for the first time. The measurement precision reached the order of 10–19 e·cm, representing an improvement of approximately three orders of magnitude over the result obtained at Fermilab in the United States in 1981. The results were published in Science under the title 'Measurement of the Λ Electric Dipole Moment with an Entangled Baryon-Antibaryon System' [1].

目前，电子、中子、原子和分子等体系的高精度实验均未发现非零EDM。相比之下，由于超子寿命极短且难以获得高极化度超子束流，超子EDM长期缺乏高精度实验检验。自费米实验室1981年首次测量Λ超子EDM以来，其测量精度在40余年间未取得提升。

To date, high-precision experiments on systems such as electrons, neutrons, atoms, and molecules have not detected a nonzero EDM. In contrast, due to the extremely short lifetime of hyperons and the difficulty in obtaining highly polarized hyperon beams, hyperon EDM has long lacked high-precision experimental tests. Since Fermilab's first measurement of the Λ hyperon EDM in 1981, its measurement precision had not improved for over 40 years.

早在1993年，马建平、何小刚等便指出，可通过研究J/ψ衰变到量子纠缠Λ和反Λ超子过程中的CP破坏效应测量Λ超子的电偶极矩，并在后续理论工作中对这一方法进行了系统发展[2,3]，为短寿命超子EDM测量提供了一条不同于自旋进动方法的新途径。在实验分析方法上，张峰等和傅金林等先后发展了基于全角分布的分析方法，不断提高对Λ超子EDM的测量灵敏度[4,5]。

As early as 1993, Ma Jianping, He Xiaogang and other researchers pointed out that the Λ hyperon EDM could be measured through CP-violating effects in J/ψ decays into quantum-entangled Λ-anti-Λ pairs, and systematically developed this method in subsequent theoretical work[2,3], providing a new avenue for measuring the EDM of short-lived hyperons that differs from the spin precession method. In terms of experimental analysis methods, Zhang Feng et al. and Fu Jinlin et al. successively developed analysis methods based on full angular distributions, continuously improving the sensitivity of Λ hyperon EDM measurement[4,5].

(a) Schematic diagram of EDM measurement via external field-induced spin precession

(b) Schematic diagram of EDM measurement with an entangled hyperon-anti-hyperon system

在上述工作的基础上，此次研究利用BESIII采集的100亿J/ψ数据开展完整角分布分析。研究未观察到显著的非零Λ超子EDM信号，测量精度达到10–19e·cm量级，较1981年的实验结果提高约三个数量级。

Building on the previous work, this study utilized 10 billion J/ψ events collected by BESIII to conduct a full angular distribution analysis. The study did not observe a significant nonzero Λ hyperon EDM signal, with a measurement precision on the order of 10-19 e·cm, improving upon the experimental results obtained in 1981 by about three orders of magnitude.

Λ超子含有奇异夸克，其EDM为探索奇异夸克相关的CP破坏效应提供了独特的实验窗口。由于不同粒子体系对潜在CP破坏来源具有不同的敏感性，Λ超子EDM与中子EDM等测量形成重要互补。将此次结果与现有中子EDM实验限制相结合，可进一步约束QCD真空角、奇异夸克EDM等基本参数，压缩潜在新物理的参数空间。此外，该研究建立了利用纠缠重子—反重子体系测量短寿命粒子EDM的新方法。这一方法可进一步推广至其他超子体系，为系统探索奇异重子中的CP破坏提供新的实验途径。

The Λ hyperon contains a strange quark, and its EDM provides a unique experimental window for exploring CP-violating effects associated with strange quarks. Since different particle systems have different sensitivities to potential sources of CP violation, measurements of the Λ hyperon EDM are an important complement to neutron EDM measurements and others. Combining this result with existing neutron EDM experimental constraints can further constrain fundamental parameters such as the QCD vacuum angle and the EDM of strange quarks, compressing the parameter space of potential new physics. Furthermore, this study establishes a new method for measuring the EDM of short-lived particles using an entangled baryon-antibaryon system. This method can be extended to other hyperon systems, providing a new experimental avenue for systematically exploring CP violation in strange baryons.

Artistic illustration of the quantum-entangled Lambda–anti-Lambda system used in the BESIII electric dipole moment measurement.

该工作由中国科学院大学、中国科学院高能物理研究所及山东大学合作完成。中国科学院大学傅金林长聘副教授、张剑宇博士为主要完成人，撰写了论文并完成了预印本（arXiv）发布和期刊投稿工作。该研究得到了中国科学院大学强子物理创新研究群体项目平台大力支持。该平台充分发挥学科协同创新作用，推动理论与实验探索深度融合，促进粒子物理、核物理和宇宙学等学科交叉，为团队围绕粒子物理与强子物理领域的前沿科学问题开展联合攻关提供了重要支撑。

This work was completed jointly by the University of Chinese Academy of Sciences, the Institute of High Energy Physics of the Chinese Academy of Sciences, and Shandong University. Fu Jinlin, tenured associate professor at UCAS, and Dr. Zhang Jianyu were the principal contributors, writing the paper and completing the preprint release on arXiv and journal submission. This research was strongly supported by the UCAS Innovative Research Group Project Platform from Hadron Physics, which gives full play to collaborative innovation across disciplines, promotes deep integration of theoretical and experimental exploration, fosters the intersection of particle physics, nuclear physics, and cosmology, and provides important support for the team to carry out joint research on frontier scientific issues in the fields of particle physics and hadron physics.

参考文献：

[1] BESIII Collaboration, "Measurement of the Λ Electric Dipole Moment with an Entangled Baryon-Antibaryon System," Science 393, 1027-1030(2026).

论文链接: https://www.science.org/doi/10.1126/science.adx7334, DOI: 10.1126/science.adx7334

[2] X.G. He, J. P. Ma, Bruce McKellar, "CP violation in J/ψ→ΛΛ" Phys. Rev. D 47, R1744–R1746 (1993).

[3] X.G. He, J.P. Ma, "Testing of P and CP symmetries with e⁺e⁻→J/ψ→ΛΛ" Phys. Lett. B 839 (2023) 137834.

[4] F. Zhang, Y. Gao, L. Huo, "An improved method for determining the electric dipole moment of Λ hyperon," Phys. Lett. B 681, 237–239 (2009).

[5] J. Fu, H.-B. Li, J.-P. Wang, F.-S. Yu, J. Zhang, "Probing hyperon electric dipole moments with a full angular analysis," Phys. Rev. D 108, L091301 (2023).

相关链接：https://www.eurekalert.org/news-releases/1142555