RUI: Study of the Nucleon Structure Using Deeply Virtual Compton Scattering at Jefferson Lab.

几十年来，了解核子结构一直是许多科学家关注的焦点。在过去的40年里，有了巨大的理论和实验进展，使我们发现了夸克作为物质的基本砖，以及支配它们相互作用的定律。广义部分子分布(GPD)是用来描述强子(由夸克和胶子组成的粒子)的组成的理论工具。这些分布提供了坐标和动量空间中完全相关的夸克信息，允许访问关键性质，如核子中夸克的角动量分布，并解释夸克如何对核子的整体性质做出贡献，如它们的电荷和轴向电荷。该项目将集中在弗吉尼亚州纽波特纽斯的托马斯·杰斐逊国家加速器设施(杰斐逊实验室)使用最近升级的连续电子束加速器设施(CEBAF)大接受光谱仪(CLAS12)进行实验。杰斐逊实验室及其“中等”能量是探索对价夸克敏感的区域的独特设施，而大接受度CLAS12探测器将允许在大的运动学范围内提取GPD。这项提议的PI是三个旨在提取GPD的实验的联合发言人。PI将在杰斐逊实验室的数据采集中发挥积极作用，并将为数据简化和分析做出贡献。本科生将参与这个项目，除了获得粒子物理数据分析的经验外，他们还将发展更广泛的技能，如编码和统计学。访问GPD的最干净的方式是通过深度虚拟康普顿散射(DVCS)，即虚拟光子与辐射真实光子的核子的单个夸克相互作用。在前旋时，软过程可用四个手性偶GPD来描述：与夸克螺旋度无关的H、E和依赖于夸克螺旋度的H-Tide和E-Tide。该项目的重点是测量具有质子和中子靶的DVCS的靶和束流不对称性以及截面。这些在不同核子上的观测数据对四种GPD的子集具有独特的敏感性，它们的同时测定允许全面提取GPD用于质子、中子和风味分解。2018年9月，非极化质子目标运行将开始，提供大量额外的生产数据。中子靶和极化质子靶的实验预计将在未来三年内进行。费尔菲尔德大学将为物理分析和数据缩减的其他方面做出贡献，如质量测试、校准和软件开发。除了新数据的工作外，当新数据可用时，费尔菲尔德大学将继续完成模拟工作，为即将到来的实验做准备，以研究探测器的最佳配置。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Understanding the structure of the nucleon has been the focus of many scientists for decades. Over the past 40 years there has been a tremendous theoretical and experimental advancement that brought us to the discovery of quarks as fundamental bricks of matter and the laws that govern their interactions. The generalized parton distributions (GPDs) are theoretical tools used to describe hadrons (particles that are made from quarks and gluons) in terms of their constituents. These distributions give fully correlated quark information in both coordinate and momentum space, allowing access to crucial properties such as the angular momentum distribution of quarks in the nucleon and explaining how quarks contribute to the overall properties of nucleons such as their electric and axial charge. This project will focus on experiments at Thomas Jefferson National Accelerator Facility (Jefferson Lab) in Newport News, VA using the recently upgraded Continuous Electron Beam Accelerator Facility (CEBAF) large acceptance spectrometer (CLAS12). Jefferson lab with its "intermediate" energies is a unique facility to explore the region sensitive to the valence quarks, and the large acceptance CLAS12 detector will allow the extraction of GPDs over large kinematic ranges. The PI of this proposal is a co-spokesperson of three experiments aimed to extraction of GPDs. The PI will take an active role in the data taking at Jefferson Lab and will contribute to the data reduction and analysis. Undergraduate students will be involved in this project and in addition to gaining experience in data analysis in particle physics, they will develop broader skills, such as coding and statistics.The cleanest way to access GPDs is via deeply virtual Compton scattering (DVCS), where the virtual photon interacts with a single quark of the nucleon radiating a real photon. At leading twist, the soft process is described by four chiral-even GPDs: the quark-helicity independent, H, E and the quark helicity dependent H-tilde and E-tilde. The focus of this project is to measure target and beam asymmetries and cross sections for the DVCS with proton and neutron targets. These observables on different nucleons have unique sensitivity to a subset of the four GPDs, and their simultaneous determination allows for a comprehensive extraction of GPDs for the proton and neutron and flavor decomposition. In September 2018, the unpolarized proton target run will start, providing a significant amount of additional production data. Experiments on the neutron target and the polarized proton target are expected to run in the next three years. Fairfield University will contribute to the physics analysis and other aspects of the data reduction such as quality tests, calibration and software development. In addition to the work on the new data, as it becomes available, Fairfield University will continue to complete simulation work in preparation to the upcoming experiments to study the optimal configuration of the detector.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.