Studies of Hadronic Structure

这个项目的重点是现代核物理的一个基础研究挑战，即根据量子色动力学(QCD)，即自然界中的强力理论，理解可见物质、质子和中子的基本组成部分的结构和相互作用。核子，是由被称为胶子的强核场的量子所限制的各种夸克组成的。为了探索核子结构，我们进行了电子散射实验，其中复杂的粒子探测器被用作强大的显微镜，以确定夸克成分的详细动力学。这反过来又为测试和理解QCD提供了重要的输入。该项目涉及四个实验活动，其中三个将在托马斯·杰斐逊国家加速器设施(TJNAF)进行，第四个将在德国美因茨的Mami Microtron进行。在TJNAF上，首先，对核子激发到Delta共振的高精度测量将揭示核子波函数中存在非球形分量的机制，重点是介子云对核子动力学的作用。第二，在一个单独的实验中，我们将探索Triton(2个中子+1个质子)和He-3(1个中子+2个质子)镜像核的深度非弹性电子散射，以确定自由质子中上价夸克动量分布与下价夸克动量分布的比率，并加深我们对核介质对这些动量分布影响的理解。第三，测量质子阈值附近的J/Psi介子电生成截面将使我们能够探索J/Psi与质子之间的非微扰胶子相互作用。这一测量可能揭示出略高于阈值的截面的增强，这可能表明共形反常贡献在QCD中所起的重要作用。在Mami微加速器上，首次高精度测量虚拟康普顿散射反应对核子共振的影响，将允许研究质子的电广义极化率，这意味着核子对外部电场的刚性响应。该实验还将允许首次探索通过纯电磁光子通道的核子激发。该项目将通过为核物理实验建造仪器，主要是在TJNAF，并通过支持国际合作研究努力，来加强研究基础设施。研究活动还将通过为核物理博士论文提供选题来促进科学教育，从而培养新一代核科学家。此外，在本科生水平上培训具有实际硬件经验的学生的机会将促进核科学教育，这对于确保社会上广泛的核科学基础知识至关重要。

This project focuses on a fundamental research challenge of modern nuclear physics, namely to understand the structure and interactions of the basic building blocks of the visible matter, protons and neutrons known collectively as nucleons, in terms of Quantum Chromodynamics (QCD), the theory of the strong forces in nature. Nucleons, are composed of a variety of quarks confined by the quanta of the strong nuclear fields known as gluons. In order to explore the nucleon structure we perform electron scattering experiments where sophisticated particle detectors are utilized as powerful microscopes in order to determine the detailed dynamics of quark constituents. This in turn provides an important input for testing and understanding QCD.This project involves four experimental activities, three of which will take place at the Thomas Jefferson National Accelerator Facility (TJNAF) while the fourth one will occur at the MAMI Microtron in Mainz, Germany. At TJNAF, first, a high precision measurement of the nucleon excitation to the Delta resonance will shed light on the mechanisms responsible for the presence of non-spherical components in the nucleon wave-function, with an emphasis on the role of the pion cloud to the nucleon dynamics. Second, in a separate experiment we will explore deep inelastic electron scattering off triton (2 neutrons + 1 proton) and helium-3 (1 neutron + 2 protons) mirror nuclei to determine the ratio of the up over down valence quark momentum distributions in a free proton, and advance our understanding of the effect of the nuclear medium on these momentum distributions. Third, a measurement of the J/Psi meson electroproduction cross section near threshold off a proton will enable us to explore the non-perturbative gluonic interaction between the J/Psi and the proton. This measurement might reveal an enhancement of the cross section just above threshold which could be indicative of the important role conformal anomaly contribution plays in QCD.At the MAMI Microtron, the first high precision measurement of the Virtual Compton Scattering reaction on the nucleon resonance will allow the investigation of the electric generalized polarizability of the proton, meaning how stiffly the nucleon responds to an external electric field. The experiment will also allow for the first exploration of the nucleon excitation through a purely electromagnetic photon channel.The project will enhance the infrastructure for research by building instrumentation for nuclear physics experiments, primarily at TJNAF, and by supporting international collaborative research efforts. The research activities will also contribute to science education by providing topics for PhD theses in nuclear physics, thus training a new generation of nuclear scientists. Furthermore, the opportunities for training students at the undergraduate level with hands on hardware experience will advance nuclear science education, which is essential to ensure a broad, basic knowledge of nuclear science in society.