The Study of Nuclear Physics with Intermediate Energy Probes

研究综述原子的全部质量几乎都集中在其微小的原子核中。原子核是由带正电荷(质子)或电中性(中子)的核子组成的。然而，这些亚原子粒子不是基本粒子，而是由夸克组成的复合体，夸克通过胶粒(胶子)的交换被强大的力结合在一起。质子和中子的性质是地球上最强作用力的表现。目前关于这种力的理论是量子色动力学。我们在南卡罗来纳大学的研究项目是基于弗吉尼亚州纽波特纽斯的托马斯·杰斐逊国家加速器设施。在那里，我们使用高能电子束和光子束以及复杂的粒子探测器作为亚原子世界的强大显微镜。我们试图回答这样的问题：核子的结构是什么？什么是什么，我们如何才能激发它的内在自由度？一旦被激发，核子以哪种方式衰变回其基态？如果核子嵌在致密的核物质中，核子的结构会改变吗？如果其他亚原子粒子是在致密的核物质中产生的，它们是否会改变其性质？对这些性质的实验研究有助于洞察强力的本质，并允许对基本理论进行严格的测试。

Research SummaryAlmost the entire mass of an atom is concentrated in its tiny nucleus. The atomic nucleus is made of nucleons, which are either positively charged (protons) or electrically neutral (neutrons). These subatomic particles, however, are not elementary but themselves composite objects made of quarks held together by the strong force via the exchange of glue particles (gluons). The properties of protons and neutrons are a manifestation of that strongest force on Earth. The present theory of that force is Quantum Chromodynamics. Our research program at the University of South Carolina is based the Thomas Jefferson National Accelerator Facility in Newport News, Virginia. There, we use high-energy electron and photon beams along with sophisticated particle detectors as powerful microscopes of the subatomic world. We try to answer questions like: What is the structure of the nucleon? What are and how can we excite its internal degrees of freedom? Once excited, in which way does the nucleon decay back to its ground state? Does the structure of the nucleon change if it is embedded in dense nuclear matter? Do other subatomic particles change their properties if they are produced in dense nuclear matter? The experimental study of these properties gives insight into the nature of the strong force and allows for rigorous tests of the underlying theory.