RUI: Fundamental Symmetries and Interactions Studies in Weak and Electromagnetic Decays

RUI：弱衰变和电磁衰变的基本对称性和相互作用研究

• 批准号: 2013557
• 负责人: Paul Voytas
• 金额: $ 15万
• 依托单位: Wittenberg University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2020
• 资助国家: 美国
• 起止时间: 2020-09-01 至 2024-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2013557&HistoricalAwards=false
• 关键词: RUI; Fundamental; Symmetries; Interactions; Studies

The Standard Model of nuclear and particle physics is remarkably successful in describing a wide range of physics topics but there are still many important unanswered questions. One crucial question has to do with differences in how matter and anti-matter behave. And the Standard Model’s description of the weak interaction, one of the four fundamental forces of nature, is believed to be incomplete. This research searches for new physics beyond the Standard Model by making precise measurements in simple systems such as in the annihilation of electrons by their anti-particles (positrons) or by measuring the beta decay of a nucleus. Three projects are proposed: one to measure the decay of positronium (an unstable bound state of an electron and a positron), and two to measure the beta decay of Carbon-14 and Fluorine-20. These projects will enable talented undergraduate students at Wittenberg University, where the proportion of women physics majors is well above the national average, to work closely with faculty on leading-edge research. The students involved in this research will develop instrumentation and computer skills important for many post-college paths in STEM fields. Further, they will learn to think independently, solve practical problems, and communicate clearly. These skills prepare them well for graduate work in physics, engineering, and related fields, and for the STEM workforce, including physics teaching.The major effort will be a high-precision search for CP violation in positronium decay, using an instrument under development with support from a previous MRI award. CP violation is described in the Standard Model (SM) through the CP-violating phase of the CKM quark mixing matrix. CP violation is necessary to explain the observed matter-antimatter asymmetry in the universe, but the level of violation present in the SM is far too small to explain this asymmetry. This has motivated searches for CP violation in a broad range of systems. Searches for new mechanisms of CP violation in observables where the SM CP-violating effects are strongly suppressed are among the most sensitive probes to search for new physics. With Michigan State University collaborators, the group is developing and will employ a highly efficient, symmetric, and high-rate-capable instrument to search for CP violation in the decay of tensor polarized positronium (Ps). The goal is to improve by an order of magnitude the current limits on a CP-violating correlation involving the spin of Ps and the momenta of the two most energetic gammas in the 3-gamma decay of Ps. The group will also complete two high precision measurements of the shapes of nuclear beta spectra as tests of the SM description of the weak interaction, that is, Vector and Axial Vector parts (V-A description) in a left-handed, maximally parity violating combination. Other, non-SM interaction forms (e.g. Tensor) give rise to shapes of nuclear beta spectra that differ from those expected from a pure V-A interaction. The group is measuring the shape of the beta spectrum of 20F to put tighter limits on such non-V-A contributions to the weak interaction. The SM also predicts a contribution (“weak magnetism” (WM)) to the shape of beta spectra due to the theory’s formulation in terms of a conserved vector current (CVC). A precision spectrum shape measurement in 14C, as well as the 20F shape measurement, will quantitatively test CVC in its strong form. The 14C experiment complements a recent high-precision measurement by the group in the 14O system.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

核物理和粒子物理的标准模型在描述广泛的物理主题方面非常成功，但仍有许多重要的未解问题。一个关键的问题与物质和反物质行为的差异有关。人们认为，标准模型对弱相互作用的描述是不完整的。弱相互作用是自然界四种基本力之一。这项研究通过在简单的系统中进行精确的测量，比如电子被它们的反粒子（正电子）湮灭或通过测量原子核的衰变，来寻找超越标准模型的新物理学。他们提出了三个项目：一个是测量正电子的衰变（电子和正电子的不稳定结合状态），另一个是测量碳14和氟20的衰变。这些项目将使维滕贝格大学（Wittenberg University）有才华的本科生能够与教师密切合作，进行前沿研究。维滕贝格大学物理学专业的女性比例远高于全国平均水平。参与这项研究的学生将发展仪器和计算机技能，这对许多STEM领域的大学毕业后的道路很重要。此外，他们将学会独立思考，解决实际问题，并清楚地沟通。这些技能为他们在物理、工程和相关领域的研究生工作以及包括物理教学在内的STEM劳动力做好了准备。主要的工作将是在正电子衰变中进行高精度的CP违逆搜索，使用一种仪器，该仪器在之前的MRI奖的支持下正在开发中。在标准模型（SM）中，通过CKM夸克混合矩阵的CP违背相来描述CP违背。CP违逆对于解释宇宙中观测到的物质-反物质不对称是必要的，但SM中存在的违逆水平太小，无法解释这种不对称。这促使人们在广泛的系统中寻找CP违背。在SM CP破坏效应被强烈抑制的可观测值中寻找CP破坏的新机制是寻找新物理最敏感的探针之一。与密歇根州立大学的合作者一起，该小组正在开发并将采用一种高效、对称、高速率的仪器来搜索张量极化正电子（Ps）衰变中的CP违背。目标是将Ps的自旋和Ps的3- γ衰变中两个最具能量的伽马的动量的违反cp相关的电流限制提高一个数量级。该小组还将完成核β谱的形状的两个高精度测量，作为弱相互作用的SM描述的测试，即左手，最大违反宇称组合中的矢量和轴矢量部分（V-A描述）。其他非sm相互作用形式（如张量）产生的核谱的形状与纯V-A相互作用所期望的形状不同。该小组正在测量20F的β谱的形状，以对这种非v - a对弱相互作用的贡献施加更严格的限制。SM还预测了一个贡献（“弱磁性”（WM））的形状的β光谱，由于该理论的公式在一个守恒矢量电流（CVC）。14C的精确光谱形状测量，以及20F形状测量，将定量测试CVC的强形式。14C实验补充了该小组最近在14O系统中进行的高精度测量。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

项目成果

Search for CP-Violation in ortho-Positronium Decay

寻找正正电子衰变中的 CP 破坏

• DOI: 10.1051/epjconf/202328201003
• 发表时间: 2023
• 期刊: EPJ Web of Conferences
• 作者: Haugen, Tom-Erik;George, Elizabeth A.;Naviliat-Cuncic, Oscar;Voytas, Paul A.
• 通讯作者: Voytas, Paul A.