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

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，但仍然有许多重要的悬而未决的问题。一个关键的问题与物质和反物质行为的差异有关。而标准模型对四种基本自然力之一的弱相互作用的描述被认为是不完整的。这项研究通过在简单的系统中进行精确的测量来寻找超越标准模型的新物理，例如通过反粒子(正电子)对电子的湮没或通过测量原子核的β衰变。提出了三个项目：一个是测量正电子(一个电子和一个正电子的不稳定束缚态)的衰变，另一个是测量碳14和氟20的β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职员工密切合作进行前沿研究。维滕贝格大学物理专业的女性比例远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，这些技能对STEMfi领域的许多大学后道路非常重要。此外，他们还将学会独立思考，解决实际问题，并清晰地沟通。这些技能为他们在物理、工程和相关fi领域的研究生工作以及STEM工作人员(包括物理教学)做好了很好的准备。主要的ff研究将是高精度地搜索正电子衰变中的CP破坏，使用一种正在开发中的仪器，该仪器得到了之前的磁共振奖的支持。在标准模型(SM)中，通过CKM夸克混合矩阵的CP破坏相来描述CP破坏。CP破坏对于解释观测到的宇宙中物质-反物质的不对称性是必要的，但SM中存在的破坏程度太小，无法解释这种不对称性。这激发了在广泛的系统中搜索CP违规的动机。在能观中寻找CP破坏的新机制是寻找新物理的最灵敏的探针之一，在那里SM CP破坏eff等被强烈地抑制。与密歇根州立大学的合作者一起，该小组正在开发并将使用一种高度高效、对称和高速率的仪器来搜索张量极化正电子(Ps)衰变中的CP破坏。我们的目标是将违反CP的关联的电流限制提高一个数量级，该关联涉及Ps的自旋和Ps的3伽马衰变中两个最高能量的伽马的动量。该小组还将完成两次高精度的核β光谱形状测量，作为对弱相互作用的SM描述的测试，即左撇子，最大宇称违反组合中的矢量和轴向矢量部分(V-A描述)。其他非SM相互作用形式(例如张量)产生的核β谱形状与纯V-A相互作用所期望的形状不同。该小组正在测量20F的β光谱的形状，以对这种对弱相互作用的非V-A贡献施加更严格的限制。SM还预测了根据守恒的矢量电流(CVC)的理论公式对β光谱形状的贡献(“弱磁性”(WM))。14C的精密光谱形状测量以及20F的形状测量将对CVC的强大形式进行定量测试。14C实验补充了该小组最近在14O系统中进行的高精度测量。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

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.