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

该奖项支持位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的一个核物理实验项目。这项实验的目的是更好地了解核物质中质子和中子成分的内部夸克和胶子结构。这项拟议的研究将使用一种直接比较氦-3和氚原子核非弹性电子散射测量的新方法，提供关于氦-3和氚原子核子内夸克动量分布的基本信息。这种方法是对斯坦福直线加速器中心过去所做的实验的补充，这些实验表明，通过从氢和氢原子核散射电子，在核子内部存在点状“部分子”。新方法将消除斯坦福方法中固有的理论不确定性。这些结果将检验长期以来对核子夸克模型和描述夸克与胶子相互作用的量子色动力学理论的预测。此外，还将拟定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中最简单、最轻核的结构和动力学的“标准模型”提供关键信息。预计该项目将为基础核物理科学的发展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和氚靶系统，以及该实验室A厅设施的磁谱仪。能量高达11吉电子伏特的未极化电子将从上述核目标散射。对于非弹性测量，将使用电子高分辨率光谱仪和翻新的BigBite光谱仪来探测散射电子。测量的氚和氦-3截面的比率将可靠地确定中子和质子结构函数的比率，并随后确定核子中上夸克和下夸克的概率分布之比。氚和氦-3截面与氚截面的比率将提供关于核环境对核子中夸克的影响的额外信息。比较这两个镜像原子核的效应被认为是全面解释这一效应的关键。对于弹性测量，强子高分辨率能谱仪也将用于探测氚反冲核。这两个氚的形状因子将通过罗森布鲁斯分离测量到大的动量转移。该小组将在项目的所有方面发挥重要作用，即i)翻新、检验和校准BigBite光谱仪，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，v)公布结果。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.