Studies of Fundamental Symmetry Breaking Effects via Precision Experiments at JLab

对称性在我们对自然的理解中起着至关重要的作用。在物理学中，它们定义了物质、辐射的基本守恒定律和一般性质，以及它们之间的相互作用。核物理和粒子物理学在过去几十年的发展表明，对称破缺效应在我们宇宙的形成和发展中也起着至关重要的作用。特别是，准标量介子(中性介子、ETA介子和ETA质介子)的寿命是由自然界中破缺的对称性定义的。对称破缺效应虽然对物质的形成非常关键，但却极其微小，需要高精度的最先进的实验才能“回顾”宇宙发展的早期阶段。PrimeX项目旨在对两种最轻基本粒子的性质进行高精度研究：中性介子和ETA介子的寿命。自然界中所谓的“手性”或“左右”对称性的破坏效应提供了这些粒子的存在，并定义了它们的寿命。在该项目PI的带领下，PrimeX合作完成了中性介子寿命精密测量的第一阶段。新的结果比粒子数据手册(PDG)中提供的当前世界平均值的精度高出两倍。这项实验的第二阶段计划在未来几年内进行，以达到提议的五倍于PDG当前价值的改善。北卡罗来纳农工州立大学(NCAT)是一所历史悠久的黑人大学，90%的学生是非洲裔美国人--尤其是在物理学方面代表性较低的学生。从2002年到现在，对NCAT的PrimeX小组的奖励允许支持和培训9名本科生、6名研究生和该小组目前的博士后。该奖项的资金将继续支持本科生和研究生，以及博士后--为他们提供处于该领域前沿的实验核物理和粒子物理学的独特机会。

Symmetries play a fundamental role in our understanding of Nature. In physics they define the basic conservation laws and general properties of matter, radiation, as well as interactions between them. Developments in nuclear and particle physics in the past several decades have shown that symmetry breaking effects also play a critical role in the formation and development of our universe. In particular, the lifetimes of pseudo-scalar mesons (neutral pions, eta and eta-prime mesons) are defined by broken symmetries in Nature. The symmetry breaking effects, though very critical for the formation of matter, are extremely small and require high precision state-of-the-art experiments to be able to "look back" at the early stages of development of the universe. The PrimEx project aims to perform high precision investigations of the properties of two of the lightest elementary particles: the lifetimes of neutral pions and eta mesons. The breaking effects of so called "chiral" or "left-right" symmetry in Nature provide the existence of these particles, as well as, define their lifetimes. The PrimEx collaboration, lead by the PI of this project, completed the first stage of the precision measurement of the neutral pion lifetime. The new result is a factor of two more precise than the current average of the world value, as presented in the Particle Data Book (PDG). The second stage of this experiment is planned to perform within the next few years to reach the proposed factor of five improvement over PDG's current value. At North Carolina A&T State University (NCAT), a historically black university, 90% of the students are African American -- students especially underrepresented in physics. Awards to NCAT's PrimEx group from 2002 to the present allowed for the support and training of 9 undergraduate students, 6 graduate students and the group's present postdoc. Funding for this award will continue to support undergraduate and graduate students, as well as a postdoc -- giving them unique opportunities in experimental nuclear and particle physics at the forefront of the field.