NSF-BSF: The Study of Nuclear Physics with Intermediate Energy Probes

虽然普通物质98%的质量是由于强大的亚原子力，但目前关于这种力的理论(量子色动力学)仍然没有完全被理解。该奖项支持通过探索物质的亚结构来研究强力。原子的几乎全部质量都集中在其微小的原子核中，该原子核由带正电的核子(质子)或带电中性的核子(中子)组成。然而，这些亚原子粒子不是基本粒子，而是由胶粒(胶子)将夸克粘合在一起的复合体。核子结构是强力的一种表现，这确实是已知的最强的力。这个项目有助于解决宇宙中大多数可见质量的起源、中子星的性质、致密核物质的性质和核子结构等关键问题。回答这些和相关的问题是一项复杂的任务，需要专门的实验观测和仔细的理论预测与测量观测相对照的检验。这项研究将有助于发现和增进对核物理的理解，并将促进教学、培训和学习。南卡罗来纳大学(USC)的核物理研究项目设在弗吉尼亚州纽波特纽斯的托马斯·杰斐逊国家加速器设施(JLab)和瑞士的保罗·谢勒研究所(PSI)。在JLab，该团队使用高能电子束和光子束，以及部分由南加州大学开发的复杂粒子探测器，作为研究重子结构和相互作用的强大显微镜。这项研究计划将继续提供关键的高精度、极化和非极化的、电和光产生的观测数据，以确定目前在强QCD中存在的问题。完整和大部分完整的介子-光产生测量将以一种几乎与模型无关的方式解决重子光谱中挥之不去的问题，特别是验证SU(6)XO(3)三夸克重子结构。或者，可以通过它们在散射过程中的相互作用来探测重子的结构。研究与奇异夸克有关的强相互作用对于理解中子星的性质是必不可少的。这个项目进行了一项全面的研究，超子的光生出氚。这组广泛的单极化和双极化观测值将从超子-核子相互作用的实验中提供长期需要的信息。由于手征对称性和多体效应的部分恢复，强子的性质在介质中发生了改变。He-4中的束缚质子电磁形状因子可能会与真空中的形状因子相比进行修改，这是该小组早期测量首次揭示的。南加州大学即将在JLab对He-4、H-2和H-1进行的实验将证实或驳斥这些结果。对这种现象的观察潜在地改变了我们看待核物质中强子及其相互作用的方式。在PSI，该团队正在准备缪斯实验。这项精密实验将通过散射介子和电子来解决质子半径之谜。这一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。

Although ninety-eight percent of the mass of ordinary matter is due to the strong subatomic force, the present theory of that force (Quantum Chromodynamics) is still not fully understood. This award supports the study of the strong force by probing the substructure of matter. Almost the entire mass of an atom is concentrated in its tiny nucleus, which is made of nucleons that are either positively charged (protons) or electrically neutral (neutrons). These subatomic particles, however, are not elementary but are themselves composite objects made of quarks held together by glue particles (gluons). The structure of nucleons is a manifestation of the strong force, which is indeed the strongest force known. This project helps to address overarching questions about the origin of most of the visible mass in the universe, the nature of neutron stars, the properties of dense nuclear matter, and the structure of nucleons. Answering these and related questions is a complex task requiring dedicated experimental observations and careful testing of theoretical predictions against measured observations. This research will help discovery in and advance understanding of nuclear physics, and will promote teaching, training, and learning. The preparation of junior scientists plays a central role in the supported activities.The nuclear physics research program at the University of South Carolina (USC) is based at the Thomas Jefferson National Accelerator Facility (JLab) in Newport News, Virginia and the Paul Scherrer Institute (PSI) in Switzerland. At JLab, the group uses high-energy electron and photon beams along with sophisticated particle detectors, that were developed, in part, at USC, as powerful microscopes to study the structure and interaction of baryons. This research program will continue to provide crucial high-precision,polarized and unpolarized, electro- and photo-production observables that will pin down present problems in strong QCD. Complete and mostly complete meson-photoproduction measurements will settle in an almost model-independent way lingering problems in baryon spectroscopy and in particular verify the SU(6)xO(3) three quark baryon structure. Alternatively, the structure of baryons can be probed through their interactions in scattering processes. The study of strong interactions involving the strange quark is essential to understand the properties of neutron stars. This project carries a comprehensive study of hyperon photo-production off deuterons. The extensive set of single- and double-polarization observables will provide long-needed information from experiments on the hyperon-nucleon interaction. The properties of hadrons are modified in the medium as a consequence of the partial restoration of chiral symmetry and many-body effects. The bound proton electromagnetic form factors in He-4 may be modified compared to those in the vacuum as revealed for the first time by the group's earlier measurements. The upcoming USC experiment on He-4, H-2, and H-1 at JLab will confirm or refute these results. The observations of such phenomena are potentially transformative in the way we view hadrons and their interactions in nuclear matter. At PSI, the group is preparing the MUSE experiment. This precision experiment will address the proton-radius puzzle by scattering muons and electrons off the proton.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.