Three-dimensional imaging of hadrons with hard exclusive reactions: advances in experiment, theory, phenomenology, and lattice QCD

TL;DR

This paper reviews recent advances in three-dimensional imaging of hadrons using Generalized Parton Distributions (GPDs), highlighting experimental, theoretical, phenomenological, and lattice QCD progress, and discusses future experimental prospects.

Contribution

It provides a comprehensive overview of recent developments in GPD theory, phenomenology, and lattice QCD, and outlines future experimental directions for hadron structure studies.

Findings

Empirical extraction of the quark pressure profile inside the proton.

Visualization of hadron structure in impact parameter space.

Progress in lattice QCD calculations of GPDs.

Abstract

Generalized Parton Distributions (GPDs) have emerged as a powerful framework for exploring the internal structure of hadrons in terms of their partonic constituents. Over the past three decades, the field has witnessed significant theoretical and experimental advancements. The interpretation of GPDs in impact parameter space offers a vivid three-dimensional visualization of hadron structure, correlating longitudinal momentum and transverse spatial distributions, thereby enabling tomographic imaging of hadrons. Furthermore, the link between GPDs and the matrix elements of the QCD energy-momentum tensor provides access to fundamental properties of hadrons, including spin decomposition and internal pressure distributions. Notably, recent analyses of Deeply Virtual Compton Scattering (DVCS) data have enabled the empirical extraction of the quark pressure profile inside the proton. This white paper presents an overview of recent developments in GPD theory and phenomenology, as well as progress in lattice QCD studies. It outlines the prospects for advancing our understanding of hadron structure through the next generation of dedicated experiments, including the extension of the Jefferson Lab 12~GeV program (and its potential 22~GeV upgrade), J-PARC, COMPASS/AMBER, LHC ultra-peripheral collisions, and the future electron-ion colliders EIC and EicC.