Structure of the Nucleon and Few-Body Nuclear Systems with Electron Scattering

该奖项支持弗吉尼亚州纽波特纽斯托马斯·杰斐逊国家加速器设施的核物理实验项目。 该实验的目标是更好地了解核物质的质子和中子成分的内部夸克和胶子结构。 拟议的研究将使用一种比较直接测量氦 3 和氚原子核非弹性电子散射的新方法，提供有关氦 3 和氚原子核内夸克动量分布的基本信息。 这种方法是对斯坦福线性加速器中心过去进行的实验的补充，该中心通过散射来自氢和氘核的电子，表明核子内部存在点状“部分子”。 新方法将消除斯坦福方法中固有的理论不确定性。 这些结果将检验核子夸克模型和量子色动力学（描述夸克和胶子之间相互作用的理论）的长期预测。 此外，还将准备一项测量氚核弹性电子散射的新提案，这将为开发描述自然界最简单、最轻原子核的结构和动力学的“标准模型”提供关键信息。 该项目预计将为基础核物理科学的进步以及研究生教育和培训做出重大贡献，提供相关科学和仪器的博士论文主题，为教育、医学物理、国土安全、高科技和国家实验室研究等职业提供所需的经验。该项目将利用杰斐逊实验室正在开发的氚、氦3和氘靶系统以及实验室A厅设施中的磁谱仪。能量高达 11 吉电子伏的非极化电子将从上述核目标中散射出来。对于非弹性测量，将使用电子高分辨率能谱仪和翻新的 BigBite 能谱仪来检测散射电子。测得的氚和氦-3 横截面的比率将可靠地确定中子与质子结构函数的比率，以及随后核子中上夸克与下夸克的概率分布的比率。氚和氦 3 横截面与氘横截面的比率将提供有关核环境对核子中夸克影响的附加信息。这两个镜像核效应的比较被认为对于充分解释这种效应至关重要。对于弹性测量，强子高分辨率光谱仪还将用于检测氚反冲核。两种氚形状因子将通过 Rosenbluth 分离来测量大动量转移。该小组将在该项目的各个方面发挥重要作用，即 i) BigBite 光谱仪的翻新、检查和校准，ii) 准备要使用的所有实验仪器，iii) 获取实验数据，iv) 数据分析，以及 v) 结果发布。参与的研究生将接触并获得硬件和软件开发方面的专业知识。

This award supports a nuclear physics experimental project at the Thomas Jefferson National Accelerator Facility in Newport News, Virginia. The goal of the experiment is a better understanding of the internal quark and gluon structure of the proton and neutron constituents of nuclear matter. The proposed research will provide fundamental information on the momentum distributions of the quarks inside the nucleons of the helium-3 and tritium atoms, using a new method of comparing directly measurements of inelastic electron scattering from helium-3 and tritium nuclei. This method is complementary to experiments done in the past at the Stanford Linear Accelerator Center, which showed the existence of point-like "partons" inside the nucleons, by scattering electrons from hydrogen and deuterium nuclei. The new method will eliminate inherent theoretical uncertainties in the Stanford method. The results will test long-standing predictions of the Quark Model of the nucleon, and of Quantum Chromodynamics, the theory describing the interactions between quarks and gluons. In addition, a new proposal will be prepared for a measurement of elastic electron scattering from the tritium nucleus, which will provide critical information for the development of a "standard model" describing the structure and dynamics of the simplest, lightest nuclei in nature. The project is expected to make significant contributions to the advancement of basic nuclear physics science, and to graduate education and training by offering doctoral dissertation topics on related science and instrumentation, which provide experience needed for careers in education, medical physics, homeland security, high technology, and national laboratories research.The project will make use of a tritium, helium-3, and deuterium target system under development at Jefferson Lab, and magnetic spectrometers in the Hall A facility of the Lab. Unpolarized electrons with energy up to 11 gigaelectronvolt will be scattered from the above nuclear targets. For the inelastic measurements, scattered electrons will be detected with the electron High Resolution Spectrometer and a refurbished BigBite Spectrometer. The ratio of the measured cross sections for tritium and helium-3 will determine reliably the ratio of the neutron to proton structure functions, and subsequently the ratio of the probability distributions for an up quark compared to a down quark in the nucleon. The ratio of the tritium and helium-3 cross sections to the deuterium cross section will provide additional information about the effect of the nuclear environment on quarks in the nucleon. A comparison of the effect for these two mirror nuclei is considered to be essential for a full explanation of this effect. For the elastic measurements, the hadron High Resolution Spectrometer will be also used for detection of tritium recoiling nuclei. The two tritium form factors will be measured up to large momentum transfers by means of a Rosenbluth separation. This group will play a major role in all aspects of the project, namely the i) refurbishment, checkout, and calibration of the BigBite spectrometer, ii) preparation of all experimental apparatuses to be used, iii) acquisition of the experimental data, iv) data analysis, and v) publication of the results. The graduate students involved will be exposed to and gain expertise with both hardware and software development.