Fundamental Studies in Nuclear Physics

对基本粒子性质进行精确的实验测试，现在是一种行之有效的方法，可以超越我们目前的物理知识，寻找新的自然规律。这个研究项目围绕着两个实验来精确测量中子的物理特性。第一个被称为UCNA的实验正在洛斯阿拉莫斯国家实验室进行，使用的是极慢中子（超冷中子，简称UCN），这种中子的能量很低，可以储存在磁性“瓶子”里。这使得实验可以精确测量中子衰变为质子、电子和反中微子粒子时电子发射的方向。这提供了有关放射性理论（也称为弱核力）所需的信息。此外，PI和他的团队正在为未来的实验开发设备，以寻找中子可能的电偶极矩（EDM）。这种EDM的存在将是一个超越我们现有知识的新物理学信号，可以帮助解释为什么宇宙是由物质主导的，而粒子物理学的标准模型预测物质和反物质的数量应该是几乎相等的。博士后学者、研究生和本科生的参与是研究计划的重要组成部分，为年轻研究人员提供了在核物理前沿领域推进他们的培训和教育的特殊机会。这个项目主要集中在自由中子基本特性的实验研究上。特别是，该小组将继续分析来自UCNA实验的数据，同时也为一个新的高灵敏度实验构建硬件，以寻找中子的EDM。UCNA实验将首次使用超冷中子对中子衰变中的β -不对称性进行高精度测量。这个量允许对弱夸克混合矩阵的统一性进行灵敏的测试，并且有可能为超越粒子相互作用标准模型的新物理学提供证据。随着最近对仪器的改进，该小组准备在此资助期间通过额外的数据采集和分析，将不对称的精度提高到~ 0.3%。新EDM实验的目标，被称为nEDM，是在橡树岭国家实验室的散裂中子源进行的，与以前的测量相比，它将把上限提高100倍；EDM信号违反时间反转和电荷宇称（CP）对称，并可能提供与宇宙物质-反物质不对称起源有关的重要信息。

Precise experimental tests of fundamental particle properties are now a well-established way to search for new laws of nature beyond our current physical knowledge. This research program centers around two experiments to make precise measurements of physical properties of the neutron. The first experiment, called UCNA, is being carried out at the Los Alamos National Laboratory, using extremely slow neutrons (ultra-cold neutrons, or UCN), which have such low energy that they can be stored in magnetic "bottles". This allows the experiment to make a precise measurement of the direction of the electron emitted when a neutron decays into a proton, an electron and a particle called an anti-neutrino. This provides needed information about the theory of radioactivity (also called the weak nuclear force). In addition, the PI and his group are developing equipment for a future experiment to search for a possible electric dipole moment (EDM) of the neutron. The existence of this EDM would be a signal of new physics beyond our current knowledge and could help to explain why the universe is dominated by matter, whereas the Standard Model of particle physics predicts there should be nearly equal amounts of matter and antimatter. Participation by postdoctoral scholars, graduate students, and undergraduates is an essential part of the research program, affording young researchers exceptional opportunities to advance their training and education in this frontier area of nuclear physics.This project is primarily focused on experimental research addressing fundamental properties of the free neutron. In particular the group will continue analyzing data from the UCNA experiment while also constructing hardware for a new, highly sensitive experiment to search for the neutron's EDM. The UCNA experiment will provide a high precision measurement of the beta-asymmetry in neutron decay using Ultra-Cold Neutrons for the first time. This quantity allows a sensitive test of the unitarity of the weak quark-mixing matrix and has the potential to provide evidence for new physics beyond the Standard Model of particle interactions. With recent improvements to the apparatus the group is poised to improve the precision on the asymmetry down to ~ 0.3% with additional data-taking and analysis during the period of this grant. The goal of the new EDM experiment, called nEDM, is being done at the Spallation Neutron Source at Oak Ridge National Laboratory and will improve the upper limit by a factor of 100 compared to previous measurements; observation of an EDM signals violation of time-reversal and charge-parity (CP) symmetry, and could provide important information related to the origin of the matter-antimatter asymmetry of the universe.