Studies of Fundamental Symmetry Breaking Effects via Precision Experiments at JLab

通过 JLab 精密实验研究基本对称破缺效应

• 批准号: 0855543
• 负责人: Ashot Gasparian
• 金额: $ 48万
• 依托单位: North Carolina Agricultural & Technical State University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2009
• 资助国家: 美国
• 起止时间: 2009-09-01 至 2014-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0855543&HistoricalAwards=false
• 关键词: Studies; Fundamental; Symmetry; Breaking; Effects

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.

对称在我们对自然的理解中扮演着重要的角色。在物理学中，它们定义了基本的守恒定律和物质、辐射以及它们之间相互作用的一般性质。过去几十年核物理和粒子物理的发展表明，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，赝标量介子（中性介子、介子和介子素数介子）的寿命是由自然界的破缺对称性定义的。对称破缺效应虽然对物质的形成至关重要，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的基本粒子的特性进行高精度的研究：中性介子和介子的寿命。自然界中所谓的“手性”或“左右”对称的断裂效应提供了这些粒子的存在，也定义了它们的寿命。由该项目的PI领导的PrimEx合作项目完成了对中性介子寿命的第一阶段精确测量。新的结果比目前粒子数据手册（PDG）中给出的世界平均值精确两倍。该实验的第二阶段计划在未来几年内进行，以达到拟议的PDG当前值的5个改进因子。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%的学生是非裔美国人——尤其是在物理专业，学生的代表性不足。从2002年到现在，国家科学技术中心的PrimEx小组获得了奖励，支持和培养了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，为他们提供在实验核物理和粒子物理领域最前沿的独特机会。