Can we determine the exact size of the nucleon?: A comprehensive study of different radii

The concept of nucleon radii plays a central role in our understanding of the internal structure of protons and neutrons, providing critical insights into the non-perturbative regime of quantum chromodynamics (QCD). While the charge radius is often interpreted as the “size” of the nucleon, this inte...

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Main Authors: Muhammad Goharipour, Fatemeh Irani, M.H. Amiri, H. Fatehi, Behnam Falahi, A. Moradi, K. Azizi
Format: Article
Language:English
Published: Elsevier 2025-08-01
Series:Nuclear Physics B
Online Access:http://www.sciencedirect.com/science/article/pii/S0550321325001713
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author Muhammad Goharipour
Fatemeh Irani
M.H. Amiri
H. Fatehi
Behnam Falahi
A. Moradi
K. Azizi
author_facet Muhammad Goharipour
Fatemeh Irani
M.H. Amiri
H. Fatehi
Behnam Falahi
A. Moradi
K. Azizi
author_sort Muhammad Goharipour
collection DOAJ
description The concept of nucleon radii plays a central role in our understanding of the internal structure of protons and neutrons, providing critical insights into the non-perturbative regime of quantum chromodynamics (QCD). While the charge radius is often interpreted as the “size” of the nucleon, this interpretation is an oversimplification that overlooks the multifaceted nature of nucleon structure. This paper provides a comprehensive overview of the different nucleon radii, including the charge and magnetic radii, the axial radius, and the emerging concepts of mechanical and mass radii. We discuss the definitions as well as the experimental, theoretical and phenomenological determinations of these radii, highlighting their distinct physical origins and implications. By synthesizing recent experimental results and theoretical advancements, we emphasize that each radius reflects a specific aspect of the nucleon's internal structure, such as its electric charge distribution, magnetic properties, weak interactions, or internal mechanical stress. In particular, we address the common but misleading interpretation of the proton radius as a simple measure of its size, underscoring the nuanced and context-dependent nature of nucleon radii. Through this exploration, we aim to clarify the roles of these radii in characterizing nucleon structure and to identify open questions that remain to be addressed. This work contributes to a deeper understanding of the nucleon and its significance in the broader context of particle and nuclear physics.
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spelling doaj-art-fda433ce9f3e46b8a954260a12eaf8882025-08-20T02:25:40ZengElsevierNuclear Physics B0550-32132025-08-01101711696210.1016/j.nuclphysb.2025.116962Can we determine the exact size of the nucleon?: A comprehensive study of different radiiMuhammad Goharipour0Fatemeh Irani1M.H. Amiri2H. Fatehi3Behnam Falahi4A. Moradi5K. Azizi6School of Physics, Institute for Research in Fundamental Sciences (IPM), P.O. Box 19395-5531, Tehran, Iran; School of Particles and Accelerators, Institute for Research in Fundamental Sciences (IPM), P.O. Box 19395-5746, Tehran, Iran; Corresponding author at: School of Physics, Institute for Research in Fundamental Sciences (IPM), P.O. Box 19395-5531, Tehran, Iran.Department of Physics, University of Tehran, North Karegar Avenue, Tehran 14395-547, IranDepartment of Physics, University of Tehran, North Karegar Avenue, Tehran 14395-547, IranDepartment of Physics, University of Tehran, North Karegar Avenue, Tehran 14395-547, IranDepartment of Physics, University of Tehran, North Karegar Avenue, Tehran 14395-547, IranDepartment of Physics, University of Tehran, North Karegar Avenue, Tehran 14395-547, IranDepartment of Physics, University of Tehran, North Karegar Avenue, Tehran 14395-547, Iran; Department of Physics, Dogus University, Dudullu-Ümraniye, 34775 Istanbul, Türkiye; School of Particles and Accelerators, Institute for Research in Fundamental Sciences (IPM), P.O. Box 19395-5746, Tehran, IranThe concept of nucleon radii plays a central role in our understanding of the internal structure of protons and neutrons, providing critical insights into the non-perturbative regime of quantum chromodynamics (QCD). While the charge radius is often interpreted as the “size” of the nucleon, this interpretation is an oversimplification that overlooks the multifaceted nature of nucleon structure. This paper provides a comprehensive overview of the different nucleon radii, including the charge and magnetic radii, the axial radius, and the emerging concepts of mechanical and mass radii. We discuss the definitions as well as the experimental, theoretical and phenomenological determinations of these radii, highlighting their distinct physical origins and implications. By synthesizing recent experimental results and theoretical advancements, we emphasize that each radius reflects a specific aspect of the nucleon's internal structure, such as its electric charge distribution, magnetic properties, weak interactions, or internal mechanical stress. In particular, we address the common but misleading interpretation of the proton radius as a simple measure of its size, underscoring the nuanced and context-dependent nature of nucleon radii. Through this exploration, we aim to clarify the roles of these radii in characterizing nucleon structure and to identify open questions that remain to be addressed. This work contributes to a deeper understanding of the nucleon and its significance in the broader context of particle and nuclear physics.http://www.sciencedirect.com/science/article/pii/S0550321325001713
spellingShingle Muhammad Goharipour
Fatemeh Irani
M.H. Amiri
H. Fatehi
Behnam Falahi
A. Moradi
K. Azizi
Can we determine the exact size of the nucleon?: A comprehensive study of different radii
Nuclear Physics B
title Can we determine the exact size of the nucleon?: A comprehensive study of different radii
title_full Can we determine the exact size of the nucleon?: A comprehensive study of different radii
title_fullStr Can we determine the exact size of the nucleon?: A comprehensive study of different radii
title_full_unstemmed Can we determine the exact size of the nucleon?: A comprehensive study of different radii
title_short Can we determine the exact size of the nucleon?: A comprehensive study of different radii
title_sort can we determine the exact size of the nucleon a comprehensive study of different radii
url http://www.sciencedirect.com/science/article/pii/S0550321325001713
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