Nuclear physics with a medium-energy Electron-Ion Collider

TL;DR

A medium-energy Electron-Ion Collider (EIC) with variable energy and high luminosity could significantly advance understanding of Quantum Chromodynamics by exploring the internal structure of nucleons and nuclei, and the process of hadron formation.

Contribution

This paper reviews the potential of a medium-energy EIC to address key QCD questions, highlighting the new insights achievable with such a collider.

Findings

Proposed EIC parameters enable detailed 3D nucleon imaging.

EIC can probe nuclear color fields and parton densities.

The collider offers new opportunities to study hadronization processes.

Abstract

A polarized ep/eA collider (Electron-Ion Collider, or EIC) with variable center-of-mass energy sqrt(s) ~ 20-70 GeV and a luminosity ~ 10^{34} cm^{-2} s^{-1} would be uniquely suited to address several outstanding questions of Quantum Chromodynamics (QCD) and the microscopic structure of hadrons and nuclei: (i) the three-dimensional structure of the nucleon in QCD (sea quark and gluon spatial distributions, orbital motion, polarization, correlations); (ii) the fundamental color fields in nuclei (nuclear parton densities, shadowing, coherence effects, color transparency); (iii) the conversion of color charge to hadrons (fragmentation, parton propagation through matter, in-medium jets). We briefly review the conceptual aspects of these questions and the measurements that would address them, emphasizing the qualitatively new information that could be obtained with the collider. Such a medium-energy EIC could be realized at Jefferson Lab after the 12 GeV Upgrade (MEIC), or at Brookhaven National Lab as the low-energy stage of eRHIC.