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问题没有得到解答。一个关键的问题与物质和反物质如何表现的差异有关。 而标准模型对自然界四种基本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系统中进行精确测量来寻找标准模型之外的新物理学，例如通过反粒子（正电子）或测量原子核的β衰变来湮灭电子。建议开展三个项目：一个用来测量正电子素的衰变（一个电子和一个正电子的不稳定结合态），两个用来测量碳-14和氟-20的β衰变。这些项目将使Wittenberg大学有才华的本科生能够与教师密切合作进行前沿研究，Wittenberg大学的女性物理专业的比例远高于全国平均水平。参与这项研究的学生将开发仪器和计算机技能，这对STEM领域的许多大学后路径非常重要。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学，工程学和相关领域的研究生工作以及STEM劳动力（包括物理教学）做好了准备。主要任务将是高精度搜索正电子素衰变中的CP破坏，使用正在开发的仪器，并获得先前MRI奖的支持。CP破坏在标准模型（SM）中通过CKM夸克混合矩阵的CP破坏相来描述。CP破坏对于解释宇宙中观察到的物质-反物质不对称性是必要的，但是SM中存在的破坏水平太小，无法解释这种不对称性。这激发了在广泛的系统中搜索CP违反。在SM CP破坏效应被强烈抑制的观测量中寻找CP破坏的新机制是寻找新物理的最敏感的探针之一。与密歇根州立大学的合作者，该小组正在开发并将采用一种高效，对称和高速率的仪器来寻找张量极化正电子素（Ps）衰变中的CP破坏。我们的目标是提高一个数量级的CP违反相关性的电流限制，涉及自旋的Ps和动量的两个最具活力的伽玛在3-伽玛衰变的Ps。该小组还将完成两个高精度的核β谱形状测量，作为弱相互作用的SM描述的测试，即左手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相互作用的预期不同。该小组正在测量20 F的β谱的形状，以更严格地限制这种非V-A对弱相互作用的贡献。SM还预测了贡献（“弱磁性”（WM））的β光谱的形状，由于理论的制定方面的保守矢量电流（CVC）。14 C中的精确光谱形状测量以及20 F形状测量将以其强形式定量测试CVC。14 C实验补充了该小组最近在14 O系统中进行的高精度测量。该奖项反映了NSF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。

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.