RUI: Testing QCD Symmetries via Precision Measurements of Light Pseudoscalar Mesons

标准模型（SM）是描述自然界基本粒子及其相互作用的理论。虽然SM已经成功地解释了迄今为止在实验室中观察到的许多现象，但它没有提供对实验事实的洞察力，例如物质对反物质的主导地位，也没有暗物质和暗能量的本质，这与星系的旋转曲线和宇宙的加速膨胀有关。因此，对物理学家来说，寻找超越标准模型的物理学是一项动机良好且重要的任务。寻找新物理学的一个好方法是测试不同相互作用中的基本对称性。该项目的目标是通过对中性粒子：中性介子和介子的精确测量来测试电磁和强相互作用中的基本对称性。中性介子的辐射衰减宽度在手性对称自发破缺和我们对QCD（描述强相互作用的理论）的理解之间起着关键作用。另一方面，eta辐射衰减宽度的测量将揭示轻夸克质量对手性对称、同位旋和SU(3)的显式对称性破缺的影响。此外，对各种罕见和禁止衰变的分支比或上限的测量将提供灵敏的探针来测试电荷共轭C，宇称P和时间反转T的违反，以及CP对称性，并寻找超越标准模型的新物理。这个项目的结果将为一些重要问题提供线索，比如：“为什么我们观测到的宇宙是由物质而不是反物质主导的？”以及“轻夸克的质量是多少？”这个项目将吸引本科生作为主要贡献者。它将创造一个研究丰富的学习环境，探索新的方法来招收未来的学生，并开发与研究相关的新课程。在国际合作中工作的学生将增加他们的国际经验并获得全球视野。

The Standard Model (SM) is a theory that describes fundamental particles in nature and the interactions between them. While the SM has been successful in explaining many phenomena observed in the laboratory to date, it offers no insight into experimental facts such as the dominance of matter over anti-matter, nor the nature of dark matter and dark energy, which are associated with the rotation curves of the galaxies and the accelerated expansion of the universe. Searching for physics beyond the Standard Model is therefore a well-motivated and important task for physicists. A good way to search for new physics is through tests of fundamental symmetries in different interactions.The goal of this project is to test fundamental symmetries in the electromagnetic and strong interactions via precision measurements on the properties of neutral particles: neutral pion and eta. The radiative decay width of the neutral pion plays a key role that bridges chiral symmetry spontaneous breaking and our understanding of QCD (a theory describing the strong interaction). On the other hand, the measurement of the eta radiative decay width will reveal the effect of explicit symmetry breakings of chiral symmetry, isospin, and SU(3) by the light-quark masses. In addition, the measurements of branching ratios or upper limits for various rare and forbidden decays of the eta will provide sensitive probes to test the violations of charge conjugation C, parity P, and time reversal T, as well as CP symmetries, and search for new physics beyond the Standard Model. The results of this project will provide clues to some important questions, such as: "why is our observed universe dominated by matter over anti-matter?", and "what are the masses of the light quarks?"This project will engage undergraduate students as key contributors. It will create a research-enriched learning environment, explore new approaches to recruiting prospective students, and develop new courses which are research related. Students working in an international collaboration will enhance their international experience and gain global perspectives.