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Experimental exploration of the 3D nucleon structure
Progress in Particle and Nuclear Physics ( IF 9.6 ) Pub Date : 2023-07-03 , DOI: 10.1016/j.ppnp.2023.104069
Stefan Diehl

Extensive experimental and theoretical explorations over the last decades showed that the nucleon (proton/neutron) is not just a simple system of 3 quarks bound by gluons, but a complex system of valence and sea quarks as well as gluons (summarized as partons) which are all interacting with each other and moving relative to each other, following the rules of quantum chromo dynamics (QCD). To understand how the properties of these colored building blocks are related to the basic properties of the nucleon like its mass, its spin or its charge, a full understanding of the relevant effective degrees of freedom and of the effective interactions at large distances is required. In the classical picture of parton dynamics in high energy interactions the description is often simplified into two cases. On the one side the classical form factors, providing a 2D picture of the transverse position distribution and on the other side, the one-dimensional picture of a fast moving nucleon as a collection of co-linearly moving quarks and gluons, described in terms of the longitudinal momentum fraction in parton distribution functions. However, recent experimental and theoretical advances during the last two decades showed, that such a simple picture is not adequate for a full description, especially if transverse spin dependent observables are involved. It turned out, that the intrinsic transverse motion of partons and also the correlation between momentum and position information have to be considered, requiring a full 3-dimensional understanding of the nucleon structure. This review will give an overview on the main experimental data for 3D nucleon structure studies, available from lepton and hadron scattering and its interpretation in terms of generalized parton distributions (GPDs) and transverse momentum dependent parton distributions (TMDs). Recent global fits of both types of distribution functions based on experimental data and their physics content will be presented and discussed on the way to a full 3D imaging of the nucleon. Furthermore, an overview of current and future trends and new perspectives in the field will be provided.



中文翻译:

3D核子结构的实验探索

过去几十年的大量实验和理论探索表明,核子(质子/中子)不仅仅是一个由胶子束缚的 3 个夸克组成的简单系统,而是一个由价夸克、海夸克以及胶子(概括为部分子)组成的复杂系统,它们都相互作用并相对运动,遵循量子色动力学(QCD)的规则。为了了解这些彩色构件的特性如何与核子的质量、自旋或电荷等基本特性相关,需要充分了解相关的有效自由度和远距离的有效相互作用。在高能相互作用中部分子动力学的经典图像中,描述通常被简化为两种情况。一方面是经典的外形尺寸,提供横向位置分布的 2D 图片,另一方面,快速移动核子的一维图像,作为共线移动夸克和胶子的集合,用部分子分布函数中的纵向动量分数来描述。然而,过去二十年的最新实验和理论进展表明,这样一个简单的图片不足以进行完整的描述,特别是在涉及横向自旋相关可观测量的情况下。事实证明,固有的横向运动 特别是如果涉及横向自旋相关的可观测量。事实证明,固有的横向运动 特别是如果涉及横向自旋相关的可观测量。事实证明,固有的横向运动必须考虑部分子以及动量和位置信息之间的相关性,需要对核子结构有完整的 3 维理解。本综述将概述 3D 核子结构研究的主要实验数据,这些数据可从轻子和强子散射中获得,并根据广义部分子分布 (GPD) 和横向动量相关部分子分布 (TMD) 进行解释。最近基于实验数据及其物理内容的两种分布函数的全局拟合将在核子的完整 3D 成像过程中进行介绍和讨论。此外,还将概述该领域当前和未来的趋势以及新观点。

更新日期:2023-07-03
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