Experimental Studies of the QCD Structure of the Neutron

所有科学中最成功的理论之一是粒子物理学的标准模型。它描述了构成可见宇宙的亚原子粒子之间的基本相互作用。在标准模型中，强力由量子色动力学（QCD）描述，这种力控制着构成质子和中子（统称为“核子”）的普通物质核中的组成粒子之间的相互作用。虽然QCD在解释核子结构的许多方面非常成功，但仍然存在许多问题。理解组成粒子（夸克和胶子）之间的基本作用力如何导致质子和中子的结构，是现代核物理学的首要目标之一。在过去的几十年里，核子结构研究中最强大的实验工具之一是原子核内核子的快电子散射。该项目将支持一个电子散射实验项目，以研究电子从单个“价”夸克散射时中子和质子的基本结构。这种情况特别有趣，因为对上下夸克分布的比例有一些明确的数学预测，精确的测量将检验我们对QCD理论的理解。此外，该研究项目还将解决培训下一代物理学家的关键需求，并为历史上代表性不足的群体提供科学培训，包括直接参与该项目的妇女和非裔美国人。在少数族裔机构的校园里，高度可见的前沿研究为学生提供了接触科学的机会，否则他们可能无法接触到这些科学。该研究计划将通过在托马斯·杰斐逊国家加速器设施（JLab）用电子束进行的两个互补实验来完成。汉普顿小组在这两个实验中都起着领导作用，每个实验都将成为汉普顿博士生的论文主题。第一个实验将通过旁观者质子标记氘靶的方法测量近自由中子结构函数和上下夸克分布的比值。汉普顿集团除了对数据分析和模拟做出贡献外，还负责反冲质子探测器的设计、建造和操作。第二次实验于2018年在C厅采集数据，测量了大Bjorken-x下质子和氘核F2的包涵结构函数。汉普顿小组参与了数据分析和模拟工作，以及对c大厅的新SHMS光谱仪的系统研究。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智力价值和更广泛的影响审查标准进行评估，被认为值得支持。

One of the most successful theories in all of science is the Standard Model of particle physics. It describes the fundamental interactions of the sub-atomic particles that make up the visible universe. Within the Standard Model, the Strong Force is described by Quantum Chromodynamics (QCD) and this force governs the interaction between the constituent particles making up the protons and neutrons (collectively "nucleons") in the nucleus of ordinary matter. While QCD has been remarkably successful in explaining many aspects of nucleon structure, many questions still remain. Understanding how the fundamental force between the constituent particles (quarks and gluons) leads to the structure of the protons and neutrons is one of the overarching ambitions of modern nuclear physics. Over the past several decades, one of the most powerful experimental tools for nucleon structure studies has been the scattering of fast electrons from nucleons inside atomic nuclei. This project will support an experimental program of electron scattering to study the fundamental structure of the neutron and proton in the case when an electron is scattered from a single "valence" quark. This case is of particular interest as there are some definite mathematical predictions for the ratio of the up to down quark distributions, and precise measurements would test our understanding of the QCD theory. In addition, this research program will address a critical need for training the next generation of physicists and provide science training to historically underrepresented groups, including women and African-Americans working directly on the project. The presence of highly visible, leading edge research on the campus of a minority institution provides students with exposure to science that might not otherwise be accessible. The research program will be accomplished via two complementary experiments carried out with the electron beam at the Thomas Jefferson National Accelerator Facility (JLab). The Hampton group has a leadership role in both experiments, and each experiment will be the dissertation topic for a Hampton Ph.D. student. The first experiment will measure the nearly free neutron structure function and the ratio of down to up quark distributions via the method of spectator proton tagging from a deuterium target. The Hampton group has responsibility for design, construction, and operation of the recoil proton detector in addition to contributions to the data analysis and simulation. The second experiment took data in 2018 in Hall C to measure the inclusive proton and deuteron F2 structure functions at large Bjorken-x. The Hampton group participated in the data analysis and simulation efforts, as well as systematic studies of the new SHMS spectrometer in Hall C.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.