# Nuclear physics at the energy frontier: recent heavy ion results from the perspective of the Electron Ion Collider

## TL;DR

This paper reviews recent heavy ion results and discusses how the upcoming Electron Ion Collider will advance understanding of nucleon structure, gluon saturation, and the limitations of current collision experiments.

## Contribution

It highlights the potential of the EIC to address open questions in nucleon structure and gluon dynamics, and critiques the limitations of current heavy ion collision data.

## Key findings

- Heavy ion results show signatures similar to gluon saturation.
- Current hadron collision experiments have kinematic limitations.
- Proton-proton and proton-nucleus collisions may not fully disentangle effects.

## Abstract

Quarks and gluons are the fundamental constituents of nucleons. Their interactions rather than their mass, is responsible for $99\%$ of the mass of all visible matter in the universe. Measuring the fundamental properties of matter has had a large impact on our understanding of the nucleon structure and it has given us decades of research and technological innovation. Despite the large number of discoveries made, many fundamental questions remain open and in need of a new and more precise generation of measurements. The future Electron Ion Collider (EIC) will be a machine dedicated to hadron structure research. It will study the content of protons and neutrons in a largely unexplored regime in which gluons are expected to dominate and eventually saturate. While the EIC will be the machine of choice to quantify this regime, recent surprising results from the heavy ion community begin to exhibit similar signatures as those expected from a regime dominated by gluons. Many of the heavy ion results that will be discussed in this document highlight the kinematic limitations of hadron-hadron and hadron-nucleus collisions. The reliability of using as a reference proton-proton (pp) and proton-Nucleus(pA) collisions to quantify and disentangle vacuum and Cold Nuclear Matter (CNM) effects from a Quark Gluon Plasma (QGP) may be under question. An selection of relevant pp and pA results which highlight the need of an EIC will be presented