Nature. 2022 Jun;606(7912):64-69. doi: 10.1038/s41586-022-04624-1. Epub 2022 Jun 1.
Though immensely successful, the standard model of particle physics does not offer any explanation as to why our Universe contains so much more matter than antimatter. A key to a dynamically generated matter-antimatter asymmetry is the existence of processes that violate the combined charge conjugation and parity (CP) symmetry. As such, precision tests of CP symmetry may be used to search for physics beyond the standard model. However, hadrons decay through an interplay of strong and weak processes, quantified in terms of relative phases between the amplitudes. Although previous experiments constructed CP observables that depend on both strong and weak phases, we present an approach where sequential two-body decays of entangled multi-strange baryon-antibaryon pairs provide a separation between these phases. Our method, exploiting spin entanglement between the double-strange Ξ baryon and its antiparticle [Formula: see text], has enabled a direct determination of the weak-phase difference, (ξ - ξ) = (1.2 ± 3.4 ± 0.8) × 10 rad. Furthermore, three independent CP observables can be constructed from our measured parameters. The precision in the estimated parameters for a given data sample size is several orders of magnitude greater than achieved with previous methods. Finally, we provide an independent measurement of the recently debated Λ decay parameter α (refs. ). The [Formula: see text] asymmetry is in agreement with and compatible in precision to the most precise previous measurement.
尽管粒子物理学的标准模型取得了巨大的成功，但它并没有解释为什么我们的宇宙中物质比反物质多得多。动态产生物质-反物质不对称性的关键是存在违反电荷共轭和宇称（CP）对称性的过程。因此，CP 对称性的精确检验可用于寻找超越标准模型的物理。然而，强子通过强过程和弱过程的相互作用而衰变，这可以用振幅之间的相对相位来量化。尽管之前的实验构建了依赖于强过程和弱过程的 CP 可观测量，但我们提出了一种方法，其中纠缠的多奇异重子-反重子对的顺序双体衰变提供了这些相位之间的分离。我们的方法利用了双奇异 Ξ 重子与其反粒子 [公式：见正文] 之间的自旋纠缠，能够直接确定弱相位差 (ξ−ξ) = (1.2 ± 3.4 ± 0.8) × 10 rad。此外，我们可以从测量的参数中构造三个独立的 CP 可观测量。对于给定的数据样本大小，估计参数的精度比以前的方法高几个数量级。最后，我们提供了对最近争议的 Λ 衰变参数 α（参考文献）的独立测量。[公式：见正文] 不对称性与以前最精确的测量结果一致，并在精度上具有兼容性。
