Studies of Hadronic Structure

强子结构研究

• 批准号: 1305536
• 负责人: Nikolaos Sparveris
• 金额: $ 21万
• 依托单位: Temple University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2013
• 资助国家: 美国
• 起止时间: 2013-07-01 至 2016-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1305536&HistoricalAwards=false
• 关键词: Studies; Hadronic; Structure

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.

该项目侧重于现代核物理学的基础研究挑战，即了解可见物质，质子和中子的基本组成部分的结构和相互作用，统称为核子，量子色动力学（QCD），自然界中的强力理论。核子，是由各种夸克组成的，被称为胶子的强核场的量子所限制。为了探索核子的结构，我们进行电子散射实验，先进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提供了一个重要的输入。该项目包括四个实验活动，其中三个将在托马斯杰斐逊国家加速器设施（TJNAF）进行，而第四个将在德国美因茨的MAMI Microtron进行。在TJNAF，首先，一个高精度的测量的核子激发的德尔塔共振将揭示的机制，负责在核子波函数中的非球形组件的存在，重点是介子云的作用，核子动力学。其次，在一个单独的实验中，我们将探索深非弹性电子散射的triton（2中子+1质子）和氦-3（1中子+2质子）镜像核，以确定在一个自由质子的上下价夸克动量分布的比例，并推进我们的理解，这些动量分布的核介质的影响。第三，测量J/Psi介子在质子阈值附近的电生截面将使我们能够探索J/Psi和质子之间的非微扰胶子相互作用。这种测量可能会揭示一个增强的横截面刚刚超过阈值，这可能是指示的重要作用，共形异常的贡献在QCD中发挥作用。在MAMI Microtron，第一次高精度测量的虚康普顿散射反应的核子共振将允许调查的电广义极化率的质子，这意味着如何僵硬的核子响应外部电场。 该实验还将首次通过纯电磁光子通道探索核子激发，该项目将加强研究基础设施，主要是在东京NAF建造核物理实验仪器，并支持国际合作研究工作。研究活动还将通过为核物理博士论文提供课题，为科学教育做出贡献，从而培养新一代核科学家。此外，在本科阶段培养学生动手硬件经验的机会将促进核科学教育，这对于确保社会对核科学的广泛基础知识至关重要。