Eur. Phys. J. A (2019) 55: 190
https://doi.org/10.1140/epja/i2019-12885-0

Review

Pion and kaon structure at the electron-ion collider

¹ University of Campinas - UNICAMP, Institute of Physics “Gled Wataghin”, 13083-859, Campinas, São Paulo, Brazil
² University of Regina, S4S 0A2, Regina, Saskatchewan, Canada
³ University of Michigan, 48109-1040, Ann Arbor, MI, USA
⁴ Catholic University of America, 20064, Washington, DC, USA
⁵ University of Illinois at Urbana-Champaign, 61801, Urbana, IL, USA
⁶ CERN, 1211, Geneva, Switzerland
⁷ Argonne National Laboratory, 60439, Lemont, IL, USA
⁸ Instituto de Física y Matemáticas, Universidad Michoacana de San Nicolás de Hidalgo, Edificio C-3, Ciudad Universitaria, C.P. 58040, Morelia, Michoacán, Mexico
⁹ European Centre for Theoretical Studies in Nuclear Physics and Related Areas (ECT*) and Fondazione Bruno Kessler Villa Tambosi, Strada delle Tabarelle 286, I-38123, Villazzano (TN), Italy
¹⁰ School of Physics, Nankai University, 300071, Tianjin, China
¹¹ Institut für Theoretische Physik, Justus-Liebig-Universität Gießen, 35392, Gießen, Germany
¹² Laboratório de Física Teórica e Computacional - LFTC, Universidade Cruzeiro do Sul / Universidade Cidade de São Paulo, 01506-000, São Paulo, SP, Brazil
¹³ Thomas Jefferson National Accelerator Facility, 23606, Newport News, VA, USA
¹⁴ Instituto Tecnológico de Aeronáutica, 12.228-900, São José dos Campos, Brazil
¹⁵ Institut für Theoretische Physik, Universität Heidelberg, Philosophenweg 16, 69120, Heidelberg, Germany
¹⁶ University of South Carolina, 29208, Columbia, SC, USA
¹⁷ Old Dominion University, 23529, Norfolk, VA, USA
¹⁸ Southern Methodist University, 75275-0175, Dallas, TX, USA
¹⁹ Iowa State University, 50011, Ames, IA, USA
²⁰ Instituto de Física Teórica, Universidade Estadual Paulista, Rua Dr. Bento Teobaldo Ferraz, 271, 01140-070, São Paulo, SP, Brazil
²¹ Michigan State University, 48824, East Lansing, MI, USA
²² Istituto Nazionale di Fisica Nucleare, Sezione di Roma, P. le A. Moro 2, I-00185, Roma, Italy
²³ University of Glasgow, G128QQ, Glasgow, Scotland, UK
²⁴ IRFU, CEA, Université Paris-Saclay, F-91191, Gif-sur-Yvette, France
²⁵ Department of Theoretical Physics and IFIC, University of Valencia and CSIC, E-46100, Valencia, Spain
²⁶ Department of Physics, Chongqing University, 401331, Chongqing, China
²⁷ School of Physics, Nanjing University, 210093, Nanjing, Jiangsu, China
²⁸ Institute for Nonperturbative Physics, Nanjing University, 210093, Nanjing, Jiangsu, China
²⁹ Department of Integrated Sciences and Centre for Advanced Studies in Physics, Mathematics and Computation, University of Huelva, E-21071, Huelva, Spain
³⁰ Institute for Advanced Simulation, Forschungszentrum Jülich and JARA, D-52425, Jülich, Germany
³¹ Departamento de Sistemas Físicos, Químicos y Naturales, Universidad Pablo de Olavide, E-41013, Sevilla, Spain
³² College of Science, Nanjing University of Posts and Telecommunications, 210023, Nanjing, China

^* e-mail: cdroberts@nju.edu.cn

Received: 6 August 2019
Accepted: 16 September 2019
Published online: 31 October 2019

Abstract

Understanding the origin and dynamics of hadron structure and in turn that of atomic nuclei is a central goal of nuclear physics. This challenge entails the questions of how does the roughly 1GeV mass-scale that characterizes atomic nuclei appear; why does it have the observed value; and, enigmatically, why are the composite Nambu-Goldstone (NG) bosons in quantum chromodynamics (QCD) abnormally light in comparison? In this perspective, we provide an analysis of the mass budget of the pion and proton in QCD; discuss the special role of the kaon, which lies near the boundary between dominance of strong and Higgs mass-generation mechanisms; and explain the need for a coherent effort in QCD phenomenology and continuum calculations, in exa-scale computing as provided by lattice QCD, and in experiments to make progress in understanding the origins of hadron masses and the distribution of that mass within them. We compare the unique capabilities foreseen at the electron-ion collider (EIC) with those at the hadron-electron ring accelerator (HERA), the only previous electron-proton collider; and describe five key experimental measurements, enabled by the EIC and aimed at delivering fundamental insights that will generate concrete answers to the questions of how mass and structure arise in the pion and kaon, the Standard Model's NG modes, whose surprisingly low mass is critical to the evolution of our Universe.