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

Abstract

A search for $CP$ violation with an entangled system of ${\Xi }^{-}{\bar{\Xi }}^{+}$ pairs is performed, using $(10,087\pm 44)\times 10^6$ $J/\psi$ events collected with the BESIII experiment. A nine-dimensional helicity amplitude is used to fit $e^{+}{e}^{-}\to J/\psi \to {\Xi }^{-}{\bar{\Xi }}^{+}$ and its subsequent decays. The ${\Xi }^{-}$ and ${\Xi }^{+}$ decay parameters are determined with higher precision compared to the best results reported so far. Furthermore, the strong phase difference, $({\delta }_P-{\delta }_S)=(0.3\pm 1.2\pm 0.2)\times 10^{-2}\text{rad}$, and the weak phase difference, $({\xi }_P-{\xi }_S)=(-0.2\pm 1.2\pm 0.1)\times 10^{-2}\text{rad}$, are directly determined. These are the most precise measurements to date. The $CP$ asymmetry observables $A_{CP}^{\Xi }=(-7.8\pm 4.8\pm 0.8)\times 10^{-3}$ and $\Delta {\varphi }_{CP}^{\Xi }=(0.6\pm 5.1\pm 0.2)\times 10^{-3}\text{rad}$ are determined, which are consistent with $CP$ conservation. In addition, independent measurements of the $\Lambda$ decay parameter and $CP$ asymmetry $A_{CP}^{\Lambda }=(-2.9\pm 4.3\pm 0.7)\times 10^{-3}$ are also obtained, which are in agreement with the previous measurements, but with much improved precision.

arXiv comment10 pages, 3 figures, consistent with the publication in Phys. Rev. Lett. 136, 201802 (2026)

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Cited by in corpus (1)

• Observation of $\Xi (1530{)}^0$ Polarization and Determination of Its Electric and Magnetic Moments in $\psi (3686)\to \Xi (1530{)}^0\bar{\Xi }(1530{)}^0$