LHCb国际协作组近日进行了重子衰变中电荷宇称对称性破缺的观察。2025年7月16日出版的《自然》杂志发表了这项成果。

粒子物理学的标准模型（最小尺度上的粒子和相互作用的理论）预测物质和反物质的相互作用不同是由于违反了电荷共轭(C)和宇称(P)的组合对称。电荷共轭将粒子转化为它们的反物质粒子，而宇称变换颠倒了空间坐标。这一预测既适用于介子（由一个夸克和一个反夸克组成），也适用于重子（由三个夸克组成）。然而，尽管已经在各种介子衰变中发现了CP破坏，但在重子（构成可观测宇宙的物质类型）中还没有观察到CP破坏。

研究组报道了利用欧洲核子研究中心(CERN)大型强子对撞机底夸克实验(LHCb)采集的数据，对美重子Λ_b⁰衰变至pK^-π⁺π^-末态过程及其CP共轭过程的研究。该衰变通过b→u或b→s夸克能级跃迁实现。

研究结果揭示了Λ_b⁰重子与其CP共轭反重子衰变率之间存在显著不对称性，据我们所知，这首次实现了重子衰变中CP破坏的观测，并证明了重子与反重子的行为差异。在标准模型中，CP破坏源于卡比博-小林-益川机制(CKM机制)，而超出标准模型的新作用力或粒子可能产生额外贡献。这一发现为探索超越标准模型的新物理开辟了新途径。

附：英文原文

Title: Observation of charge–parity symmetry breaking in baryon decays

Author: X. Yang.

Issue&Volume: 2025-07-16

Abstract: The Standard Model of particle physics—the theory of particles and interactions at the smallest scale—predicts that matter and antimatter interact differently due to violation of the combined symmetry of charge conjugation (C) and parity (P). Charge conjugation transforms particles into their antimatter particles, whereas the parity transformation inverts spatial coordinates. This prediction applies to both mesons, which consist of a quark and an antiquark, and baryons, which are composed of three quarks. However, despite having been discovered in various meson decays, CP violation has yet to be observed in baryons, the type of matter that makes up the observable Universe. Here we report a study of the decay of the beauty baryon Λb0 to the pKπ+π final state, which proceeds through b→u or b→s quark-level transitions, and its CP-conjugated process, using data collected by the Large Hadron Collider beauty experiment1 at the European Organization for Nuclear Research (CERN). The results reveal significant asymmetries between the decay rates of the Λb0 baryon and its CP-conjugated antibaryon, providing, to our knowledge, the first observation of CP violation in baryon decays and demonstrating the different behaviours of baryons and antibaryons. In the Standard Model, CP violation arises from the Cabibbo–Kobayashi–Maskawa mechanism2, and new forces or particles beyond the Standard Model could provide further contributions. This discovery opens a new path in the search for physics beyond the Standard Model.

DOI: 10.1038/s41586-025-09119-3

Source: https://www.nature.com/articles/s41586-025-09119-3