NSF-BSF: Exploring the Proton Radius Puzzle and Phenomena Beyond the Standard Model with Low-energy Lepton Scattering

该奖项为汉普顿大学的Michael Kohl博士和他的团队提供资金，汉普顿大学是美国弗吉尼亚州的一所历史悠久的黑人学院和大学。该小组在瑞士Paul-Scherrer研究所准备的μ子散射实验（MUSE）和美国托马斯杰斐逊国家加速器设施（杰斐逊实验室）的DarkLight项目中发挥核心作用。MUSE项目是对所谓的质子半径谜题的专门研究，这是核物理学中一个非常突出的话题。实验将通过轻子-质子弹性散射高精度测量质子电荷半径，并在基本水平上比较两种电荷的介子和电子与质子的相互作用。这个实验将严格限制对这个谜题的可能解释，并有可能揭示超出标准模型的新物理学。杰斐逊实验室正在准备的暗光实验旨在发现一种与第五种相互作用相关的新粒子，这种相互作用适合于解释粒子物理学中观察到的几种异常现象，同时提供与暗物质的联系。这两个项目都为国际核与粒子物理研究前沿的学生和博士后提供了备受瞩目的机会。PI的研究项目有很多方面，为国内外的前沿教育和研究提供了很好的机会。该提案结合了汉普顿大学最先进的探测器开发及其在PSI和杰斐逊实验室的前沿研究中的应用。这为少数民族学生（主要是非裔美国人）和博士后研究人员在一流的研究设施中提供了新的研究和教育机会。在MUSE和暗光环境中开发和运行GEM探测器将有利于推进这一仍然新颖的技术，并具有潜在的未来应用于其他实验以及医疗领域。MUSE实验已经被提出并被批准，为解释所谓的质子半径之谜提供了关键的见解——质子电荷半径测量在电子探针和介子探针之间分别超过五个标准差的差异。可能的解释还包括标准模型之外的新物理学。MUSE实验旨在解决迄今为止核与粒子科学中最紧迫的问题之一。MUSE利用任意一种电荷（mu+, e+, mu-, e-）的混合μ子和电子束精确测量轻子-质子弹性散射截面和质子形状因子，目的是提取每个探针的质子电荷半径。它将以最高的精度，独立和结论性地确定，如果在电子散射和介子散射中观察到任何质子电荷半径差异。同时，它将确定双光子交换的作用，并提供严格的理论约束。Kohl博士是MUSE项目的共同发起人之一。Kohl博士的团队在MUSE中的角色对这个项目至关重要。该项目专注于在MUSE上使用GEM探测器进行高分辨率光束粒子跟踪的挑战性任务，以一种在低光束能量下从未做过的方式。跟踪器暴露在高速率密度和波束通量下，需要在几千赫的触发率下有效运行。杰斐逊实验室的DarkLight Phase-I项目包括在17 MeV/c2左右的质量区域集中寻找暗光子或中性玻色子，在那里已经报道了第五力载体的证据。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。

This award provides funding for Dr. Michael Kohl and his group at Hampton University, a Historically Black College und University in Virginia, USA. The group has a core function in the Muon Scattering Experiment (MUSE) in preparation at Paul-Scherrer Institute in Switzerland, and in the DarkLight project at the Thomas Jefferson National Accelerator Facility (Jefferson Laboratory) in the US. The MUSE project is a dedicated investigation of the so-called proton radius puzzle, a very prominent topic in nuclear physics. The experiment will measure the proton charge radius with high precision via lepton-proton elastic scattering, and will compare the interactions of muons and electrons of either charge with the proton at a fundamental level. The experiment will severely constrain possible explanations of the puzzle and has the potential to reveal new physics beyond the Standard Model. The DarkLight experiment in preparation at Jefferson Lab aims to discover a new particle associated with a fifth interaction suited to explain several observed anomalies in particle physics while offering a connection to dark matter. Both projects offer high-profile opportunities for students and postdocs at the forefront of international nuclear and particle physics research. The PI's research program has many facets and offers excellent opportunities for cutting-edge education and research purpose domestically and abroad. This proposal combines state-of-the-art detector development at Hampton University with its application in forefront research at PSI and at Jefferson Lab. This provides new research and educational opportunities at first-class research facilities for students from minority populations, predominantly African-Americans, and postdoctoral researchers. The development and operation of GEM detectors in the MUSE and DarkLight environments will be beneficial to advance this still novel technology with potential future applications in other experiments, as well as in the medical sector. The MUSE experiment has been proposed and approved to provide key insight in the quest to explain the so-called proton radius puzzle - the over five-standard deviation discrepancy between proton charge radius measurements with electronic and muonic probes, respectively. Possible explanations also include new physics beyond the Standard Model. The MUSE experiment aims to address one of the most pressing questions in nuclear and particle science to date. MUSE uses mixed muon and electron beams of either charge (mu+, e+, mu-, e-) to make precise measurements of the lepton-proton elastic scattering cross sections and proton form factors, with the goal to extract the proton charge radius for each probe. It will determine with the highest precision, model independently and conclusively, if there is any proton charge radius difference observed in electron versus muon scattering. At the same time it will determine the role of two-photon exchange and provide tight constraints on theory. Dr. Kohl is one of the co-initiators of the MUSE project. The role of Dr. Kohl's group in MUSE is essential to this project. This project focuses on the challenging task of high-resolution beam particle tracking at MUSE with GEM detectors, in a way not done before at low beam energies. The tracker is exposed to high rate density and beam flux, and needs to operate efficiently at a trigger rate of a few kHz. The DarkLight Phase-I project at Jefferson Lab includes a focused search for a dark photon or neutral boson in the mass region around 17 MeV/c2, where evidence for a fifth-force carrier has been reported.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.