# Pion and Kaon Structure at the Electron-Ion Collider

## TL;DR

This paper discusses how the Electron-Ion Collider can advance understanding of hadron mass origins and structure, focusing on pions and kaons, through experimental measurements and theoretical analysis in QCD.

## Contribution

It highlights the unique capabilities of the EIC for probing hadron structure and mass generation, emphasizing the need for integrated experimental and theoretical efforts.

## Key findings

- Identification of key measurements at the EIC for hadron structure
- Comparison of EIC capabilities with previous colliders like HERA
- Insights into the mass budget of pions and protons

## 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 1 GeV 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.