Investigating Hadron Structure at Low and Medium Energies

研究低能和中能的强子结构

• 批准号: SAPIN-2022-00025
• 负责人: Hornidge, David
• 金额: $ 3.42万
• 依托单位: Mount Allison University
• 依托单位国家: 加拿大
• 项目类别: Subatomic Physics Envelope - Individual
• 财政年份: 2022
• 资助国家: 加拿大
• 起止时间: 2022-01-01 至 2023-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=762492
• 关键词: Investigating; Hadron; Structure; Low; Medium

The objective of this research proposal is to conduct a program of precision hadron-structure experiments with electromagnetic probes at low and intermediate energies. In this energy region the description of structure and reaction dynamics encompasses nucleon/meson-based models and transitions to QCD-inspired models (or effective theories) based on quark/gluon degrees of freedom. Understanding hadronic structure in both the low-energy and transition regions of non-perturbative QCD remains at the forefront of worldwide efforts in nuclear physics. This program will focus on complementary experiments at three different laboratories: the Mainz Microtron (MAMI) in Germany, Jefferson Laboratory (JLab) in Virginia, and the High-Intensity Gamma Source (HIGS) based at Duke University in North Carolina. Our main focus over the past decade has been the study of polarizabilities, which are fundamental structure quantities like mass and charge except that they characterize a particle's internal response to an external electromagnetic field. They are of interest not only in the study of hadron structure where they can provide input to the QCD puzzle, but also in other fields such as precision atomic physics and astrophysics; for example, they yield an appreciable correction to the proton charge radius via Lamb shift and hyperfine structure in addition to defining neutron star properties. In Mainz, we will continue our leadership role in the polarizability and hadron-structure program in the A2 Collaboration; at JLab we will participate in measurements of the charged- and neutral-pion polarizabilities via the Primakoff effect using the GlueX detector in Hall D; and at HIGS we will make use of the high-flux free-electron laser to conduct lower-energy Compton scattering measurements on protons and light nuclei. At MAMI and HIGS we will concentrate on 1) light-nuclei experiments to improve the accuracy of the neutron scalar polarizabilities and 2) measurements of single- and double-polarization observables to access higher-order nucleon spin polarizabilities. In addition, we are involved in a measurement of elastic electron-proton scattering in Mainz using a new time-projection chamber (TPC), in order to better understand the low-Q^2 behaviour of the proton electric form factor and to help clarify the proton radius puzzle. Our group (HQP and PI) will contribute predominantly to data acquisition and analysis while also contributing to detector development, testing, and commissioning.

这项研究计划的目的是用中低能量的电磁探头进行精密强子结构实验。在这个能区，对结构和反应动力学的描述包括基于核子/介子的模型和基于夸克/胶子自由度的QCD激发模型(或有效理论)的过渡。了解非微扰QCD的低能区和过渡区的强子结构仍然是世界核物理努力的前沿。该计划将侧重于三个不同实验室的互补性实验：德国的美因茨微加速器(Mami)、弗吉尼亚州的杰斐逊实验室(JLab)和北卡罗来纳州杜克大学的高强度伽马源(HIGS)。在过去的十年里，我们主要关注的是极化率的研究，极化率是像质量和电荷一样的基本结构量，但它们表征了粒子对外部电磁场的内部反应。它们不仅对强子结构的研究感兴趣，因为它们可以为QCD之谜提供输入，而且还在其他领域，如精密原子物理和天体物理；例如，除了定义中子星的性质外，它们还通过Lamb位移和超精细结构对质子电荷半径进行了明显的修正。在美因茨，我们将继续在A2合作的极化率和强子结构计划中发挥领导作用；在JLab，我们将使用D厅的GlueX探测器参与通过Primakoff效应测量带电和中性介子的极化率；在HIGS，我们将利用高通量自由电子激光对质子和轻核进行较低能量的康普顿散射测量。在MAMI和HIGS，我们将专注于1)轻核实验以提高中子标量极化率的准确性，以及2)测量单极化和双极化观测值以获得更高阶的核子自旋极化率。此外，我们还利用一种新的时间投影室(TPC)对美因茨的弹性电子-质子散射进行了测量，以便更好地理解质子电子形状因子的低Q^2行为，并帮助阐明质子半径之谜。我们的团队(HQP和PI)将主要为数据采集和分析做出贡献，同时也为探测器的开发、测试和调试做出贡献。