TY - JOUR

T1 - Precise Measurement of Matter-Antimatter Asymmetry with Entangled Hyperon-Antihyperon Pairs

AU - BESIII Collaboration

AU - Ачасов, Михаил Николаевич

AU - Мучной, Николай Юрьевич

AU - Николаев, Иван Борисович

N1 - Thanks to Jusak Tandean for useful discussions about the theoretical approaches related to the strong phase difference. The BESIII Collaboration thanks the staff of BEPCII [49] and the IHEP computing center for their strong support. This work is supported in part by National Key R&D Program of China under Contracts No. 2023YFA1606000, No. 2023YFA1606704; National Natural Science Foundation of China (NSFC) under Contracts No. 12247101, No. 11635010, No. 11935015, No. 11935016, No. 11935018, No. 12025502, No. 12035009, No. 12035013, No. 12061131003, No. 12192260, No. 12192261, No. 12192262, No. 12192263, No. 12192264, No. 12192265, No. 12221005, No. 12225509, No. 12235017, and No. 12361141819; the Fundamental Research Funds for the Central Universities No. lzujbky-2025-ytA05, No. lzujbky-2025-it06, and No. lzujbky-2024-jdzx06; the Natural Science Foundation of Gansu Province No. 22JR5RA389 and No. 25JRRA799; the “111 Center” under Grant No. B20063; Beijing Natural Science Foundation of China (BNSF) under Contract No. IS23014; the Chinese Academy of Sciences (CAS) Large-Scale Scientific Facility Program; the Strategic Priority Research Program of Chinese Academy of Sciences under Contract No. XDA0480600; CAS under Contract No. YSBR-101; 100 Talents Program of CAS; The Institute of Nuclear and Particle Physics (INPAC) and Shanghai Key Laboratory for Particle Physics and Cosmology; ERC under Contract No. 758462; German Research Foundation DFG under Contract No. FOR5327; Istituto Nazionale di Fisica Nucleare, Italy; Knut and Alice Wallenberg Foundation under Contracts No. 2021.0174 and No. 2021.0299; Ministry of Development of Turkey under Contract No. DPT2006K-120470; National Research Foundation of Korea under Contract No. NRF-2022R1A2C1092335; National Science and Technology fund of Mongolia; Polish National Science Centre under Contract No. 2024/53/B/ST2/00975; STFC (United Kingdom); Swedish Research Council under Contract No. 2019.04595; the Olle Engkvist Foundation under Contract No. 200-0605; U.S. Department of Energy under Contract No. DE-FG02-05ER41374.

PY - 2026/5/18

Y1 - 2026/5/18

N2 - A search for CP violation with an entangled system of Ξ−Ξ¯ þ pairs is performed, using ð10; 087 44Þ × 106 J=ψ events collected with the BESIII experiment. A nine-dimensional helicity amplitude is used to fit eþe− → J=ψ → Ξ−Ξ¯ þ and its subsequent decays. The Ξ− and Ξ¯ þ decay parameters are determined with higher precision compared to the best results reported so far. Furthermore, the strong phase difference, ðδP − δSÞ¼ð0.3 1.2 0.2Þ × 10−2 rad, and the weak phase difference, ðξP − ξSÞ¼ ð−0.2 1.2 0.1Þ × 10−2 rad, are directly determined. These are the most precise measurements to date. The CP asymmetry observables AΞ CP ¼ð−7.84.80.8Þ×10−3 and ΔϕΞ CP ¼ð0.65.10.2Þ×10−3 rad are determined, which are consistent with CP conservation. In addition, independent measurements of the Λ decay parameter and CP asymmetry AΛ CP ¼ð−2.9 4.3 0.7Þ × 10−3 are also obtained, which are in agreement with the previous measurements, but with much improved precision.

AB - A search for CP violation with an entangled system of Ξ−Ξ¯ þ pairs is performed, using ð10; 087 44Þ × 106 J=ψ events collected with the BESIII experiment. A nine-dimensional helicity amplitude is used to fit eþe− → J=ψ → Ξ−Ξ¯ þ and its subsequent decays. The Ξ− and Ξ¯ þ decay parameters are determined with higher precision compared to the best results reported so far. Furthermore, the strong phase difference, ðδP − δSÞ¼ð0.3 1.2 0.2Þ × 10−2 rad, and the weak phase difference, ðξP − ξSÞ¼ ð−0.2 1.2 0.1Þ × 10−2 rad, are directly determined. These are the most precise measurements to date. The CP asymmetry observables AΞ CP ¼ð−7.84.80.8Þ×10−3 and ΔϕΞ CP ¼ð0.65.10.2Þ×10−3 rad are determined, which are consistent with CP conservation. In addition, independent measurements of the Λ decay parameter and CP asymmetry AΛ CP ¼ð−2.9 4.3 0.7Þ × 10−3 are also obtained, which are in agreement with the previous measurements, but with much improved precision.

KW - Hadronic decays

KW - Spin polarization

KW - Baryons

KW - Hyperons

KW - Strange quark

KW - CP violation

KW - Polarization

KW - Precision measurements

UR - https://www.scopus.com/pages/publications/105039314456

U2 - 10.1103/c1fz-9r8q

DO - 10.1103/c1fz-9r8q

M3 - Article

VL - 136

JO - Physical Review Letters

JF - Physical Review Letters

SN - 0031-9007

IS - 20

M1 - 201802

ER -