Investigating the Nucleon with Electromagnetic Probes

质子是物质的基本组成部分之一，即使在发现100年后，它们仍然没有被完全理解。事实上，质子的精确半径是一个谜，对这个量的多次测量并不完全一致。 质子半径的精确测量是重要的，因为它决定了与其他粒子的相互作用以及散射的横截面。 质子的半径甚至影响氢原子的原子光谱，这与里德伯常数的值密切相关，里德伯常数对所有原子光谱的解释至关重要，因为电子和质子波函数重叠，半径是确定重叠量的重要参数。 2010年，使用μ子氢（电子被μ子取代的氢）测量了质子的半径。这被证明是有史以来对质子半径最精确的实验测定，但与当时公认的质子半径值大不一致。这被称为质子半径之谜（PRP）。从一开始，许多物理学家就试图解决PRP，但都无济于事。MUSE（μ子质子散射实验）将通过弹性μ子散射进行世界上第一次质子半径测量，其精度可以解决这4%的半径差异。 该项目的重点是监测和维护数据采集系统，该系统读取MUSE探测器系统;并分析所得数据，以比较散射截面、形状因子和半径，并提取电荷不对称性。MUSE实验已经完全建成，该项目将支持工程运行，以进一步校准和测试设备，然后进行12个月的测量。测量将在保罗谢勒研究所的PiM 1束线上进行，该束线提供3.3 MHz的二级束，其中混合了π介子、μ介子和电子。束流动量约为117 MeV/c、160 MeV/c和210 MeV/c。这些测量将覆盖0.002 - 0.07 GeV 2的Q2范围。在上述活动中，本科生，博士生和博士后研究人员将接受现代电子系统和现代数据分析技术开发的培训。PI将介绍这项工作，作为她参与全国组织委员会主席线的会议本科妇女在物理学。这个奖项反映了NSF的法定使命，并已被认为是值得通过评估使用基金会的智力价值和更广泛的影响审查标准的支持。

Protons are one of the basic building blocks of matter and even 100 years after their discovery, they are still not fully understood. In fact, the precise radius of the proton is a puzzle and multiple measurements of this quantity do not all agree. A precise measurement of a proton’s radius is important because it determines the interaction with, and cross-section for scattering, other particles. The proton’s radius even affects the atomic spectroscopy of the hydrogen atom, which is tightly linked to the value of the Rydberg constant that has been so critical to the interpretation of all atomic spectra, because the electron and proton wave functions overlap and the radius is an important parameter in determining the amount of overlap. In 2010, a measurement of the radius of the proton was made using muonic hydrogen (hydrogen where the electron has been replaced by a muon). This proved to be the most precise experimental determination of the proton radius ever made, but was massively inconsistent with the accepted value for the proton radius at that time. This became known as the Proton Radius Puzzle (PRP). Since its inception, many physicists have tried to resolve the PRP, to no avail. MUSE (the MUon proton Scattering Experiment) will make the world’s first measurement of the proton radius via elastic muon scattering at a precision which can address this 4% radius discrepancy. The focus of this project is the supervision and maintenance of the data acquisition system which reads out the MUSE detector system; and the analysis of the resulting data to compare scattering cross sections, form factors, and radii, and to extract charge asymmetries. The MUSE experiment has been fully constructed and this project will support engineering runs to further calibrate and test the equipment, followed by 12 months of measurement. Measurements will take place in the Paul Scherer Institute PiM1 beam line, which affords a 3.3 MHz secondary beam with a mixture of pions, muons and electrons. The beam momenta will be approximately 117MeV/c, 160 MeV/c, and 210 MeV/c. These measurements will cover a Q2 range of 0.002 – 0.07 GeV2.In the course of the above described activities, undergraduate students, PhD students, and postdoctoral researchers will be trained in the development of modern electronics systems and modern data analysis techniques. The PI will present this work as part of her involvement in the National Organizing Committee Chair Line of the Conferences for Undergraduate Women in Physics.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.