Collaborative Research: Equipment for and Running of the PSI MUSE Experiment

亚原子物理学的一个基本目标是精确测定质子和中子等亚原子粒子的物理性质。 质子的半径就是这些性质之一。半径可以通过散射电子或称为μ子的较重粒子来测量。另一种技术是测量氢的能级，氢原子由一个质子加一个电子组成，或μ子氢原子由一个质子和一个μ子取代的电子组成。到目前为止，半径是通过质子对电子的散射，以及氢和μ子氢的能级来测量的。 从μ介子氢的能级测量得到的质子半径与从氢的能级测量得到的半径不一致，也与通过电子散射测量得到的质子半径不一致，这一问题被称为“质子半径之谜”。“这种差异引起了广泛的关注，因为它可能表明μ子和电子之间存在以前未观察到的和意想不到的差异。 一个专门的MUon质子散射实验（MUSE）将在瑞士的Paul Scherrer研究所运行，并直接比较质子的μ子和电子的散射，该领域的专家对其解决这个难题的潜力寄予厚望。该项目将涵盖MUSE实验探测器几个关键组件的原型设计和开发。该项目将涉及在本科生、研究生、博士后和初级教员各级培训学生和青年科学家。参与该项目的机构培训了大量各类学生，包括少数民族学生。他们在基础研究过程中接受的培训导致了从医学物理到国家安全等各个领域的职业生涯，此外还继续从事基础物理研究。MUSE实验将拓宽美国学生的视野，让他们在国际实验室进行国际合作，这将使他们有效地为成为下一代杰出的全球科学家做好准备。随着人们对质子半径之谜的广泛兴趣，MUSE有可能在当前科学界之外产生广泛的启发性。

A fundamental goal of subatomic physics is the precise determination of the physical properties of subatomic particles such as the proton and neutron. The radius of the proton is one of these properties. The radius can be measured by scattering electrons, or heavier particles called muons, off protons. Another technique is to measure the energy levels of hydrogen, an atom consisting of a proton plus an electron, or muonic hydrogen, an atom consisting of a proton with the electron replaced by a muon. To date, the radius has been measured by scattering of electrons off protons, and by the energy levels of hydrogen and muonic hydrogen. The proton radius derived from the measurement of the energy levels in muonic hydrogen disagrees with the radius derived from the measurements of the energy levels in hydrogen, and with the measurements of the proton radius by scattering of electrons, an issue known as "the proton radius puzzle." The discrepancy has attracted wide attention, because it may indicate the existence of previously unobserved and unexpected differences between the interactions of muons and electrons. A dedicated MUon proton Scattering Experiment (MUSE), which will run at the Paul Scherrer Institute in Switzerland and directly compare the scattering of muons and electrons from protons, is highly anticipated by experts in the field for its potential to resolve the puzzle. This project will cover the prototyping and development of several crucial components of the MUSE experiment detectors. The project will involve the training of students and young scientists, at the undergraduate, graduate, post-doctoral, and junior faculty levels. The institutions involved in the project have trained large numbers of students of each type, including from minority populations. The training they have received in the process of doing basic research has led to careers in a variety of areas, from medical physics to national security, in addition to continued work in fundamental physics research. The MUSE experiment will broaden the perspective of American students by having them work in an international collaboration at an international laboratory, which will prepare them effectively to become prominent global scientists of the next generation. With the broad interest in the proton radius puzzle, MUSE has the potential to be broadly inspirational beyond the current scientific community.