Eur. Phys. J. A (2025) 61: 131
https://doi.org/10.1140/epja/s10050-025-01552-2

Regular Article - Experimental Physics

Exploring baryon resonances with transition generalized parton distributions: status and perspectives

¹ Justus Liebig Universität Gießen, 35390, Gießen, Germany
² University of Connecticut, 06269, Storrs, CT, USA
³ Kyungpook National University, 41566, Daegu, Korea
⁴ NRC “Kurchatov Institute”-PNPI, 188300, Gatchina, Russia
⁵ Thomas Jefferson National Accelerator Facility, 23606, Newport News, VA, USA
⁶ Institut für Theoretische Physik, Universität Regensburg, 93040, Regensburg, Germany
⁷ Institute of Physics, Academia Sinica, 11529, Taipei, Taiwan
⁸ Physics Department, Temple University, 19122-1801, Philadelphia, PA, USA
⁹ Nuclear Science Division, Lawrence Berkeley National Laboratory, 94720, Berkeley, CA, USA
¹⁰ Department of Physics, Pukyong National University (PKNU), 48513, Busan, Korea
¹¹ University of Wuppertal, 42097, Wuppertal, Germany
¹² Department of Mathematics, Physics, and Computer Science, Faculty of Science, Japan Women’s University, 112-8681, Tokyo, Japan
¹³ Theory Center, Institute of Particle and Nuclear Studies, KEK, 305-0801, Tsukuba, Ibaraki, Japan
¹⁴ Department of Physics, Pusan National University, 46241, Busan, Korea
¹⁵ Asia Pacific Center for Theoretical Physics, POSTECH, 37673, Pohang, Korea
¹⁶ Physics Department, University of Virginia, 22904-4714, Charlottesville, VA, USA
¹⁷ University College Dublin, School of Physics, Science Centre Belfield Dublin 4, Dublin, Ireland
¹⁸ Department of Physics, Inha University, 22212, Incheon, Korea
¹⁹ National Centre for Nuclear Research (NCBJ), 02-093, Warsaw, Poland
²⁰ University of Regina, S4S 0A2, Regina, SK, Canada
²¹ Universidad de Alcalá, 28801, Alcalá de Henares, Spain
²² Institut für Kernphysik and PRISMA+ Cluster of Excellence, Johannes Gutenberg Universität, 55099, Mainz, Germany
²³ DPhN/Irfu, CEA Saclay, 91191, Gif sur Yvette, France

^a stefan.diehl@exp2.physik.uni-giessen.de, sdiehl@jlab.org

Received: 25 May 2024
Accepted: 25 March 2025
Published online: 6 June 2025

Abstract

QCD gives rise to a rich spectrum of excited baryon states. Understanding their internal structure is important for many areas of nuclear physics, such as nuclear forces, dense matter, and neutrino-nucleus interactions. Generalized parton distributions (GPDs) are an established tool for characterizing the QCD structure of the ground-state nucleon. They are used to create 3D tomographic images of the quark/gluon structure and quantify the mechanical properties such as the distribution of mass, angular momentum, and forces in the system. Transition GPDs extend these concepts to $N\to N^{\ast }$ transitions and can be used to characterize the 3D structure and mechanical properties of baryon resonances. They can be probed in high-momentum-transfer exclusive electroproduction processes with resonance transitions $e+N\to e^{\prime }+M+N^{\ast }$, such as deeply-virtual Compton scattering ($M=\gamma$) or meson production ($M=\pi ,K$, etc.), and in related photon/hadron-induced processes. This White Paper describes a research program aiming to explore baryon resonance structure with transition GPDs. This includes the properties and interpretation of the transition GPDs, theoretical methods for structures and processes, first experimental results from JLab 12 GeV, future measurements with existing and planned facilities (JLab detector and energy upgrades, COMPASS/AMBER, EIC, EicC, J-PARC, LHC ultraperipheral collisions), and the theoretical and experimental developments needed to realize this program.