Study of the Fundamental Structure of Matter with an Electron-Ion Collider

TL;DR

The paper advocates building an Electron-Ion Collider (eRHIC) to probe the fundamental structure of matter with polarized and unpolarized electron–nucleus and electron–proton collisions. It surveys the current understanding of DIS, nucleon spin, and nuclear modifications, and outlines the CGC/saturation context, while presenting a detailed physics case for EIC measurements of F_L, g1, Δg, SIDIS flavor separation, GPDs via DVCS, and polarized photon structure. It also discusses accelerator and detector designs enabling wide kinematic coverage, high luminosity, and 3D imaging of partons, aiming to address open questions about mass generation, spin origin, and parton dynamics in dense QCD matter. The work highlights how an EIC would extend QCD tests into new regimes, providing precise constraints on parton distributions, spin structure, and space-time correlations in hadrons and nuclei. Overall, the proposal envisions transformative insights into the internal landscape of protons and nuclei, advancing our understanding of strong interactions.

Abstract

We present an overview of the scientific opportunities that would be offered by a high-energy electron-ion collider. We discuss the relevant physics of polarized and unpolarized electron-proton collisions and of electron-nucleus collisions. We also describe the current accelerator and detector plans for a future electron-ion collider.

Figures (21)

• Figure 1: The center-of-mass energy vs. luminosity of the proposed Electron-Ion Collider eRHIC compared to other lepton scattering facilities.
• Figure 2: The $x$-$Q^2$ range of the proposed lepton-ion collider at Brookhaven National Laboratory (eRHIC) in comparison with the past & present experimental DIS facilities. The left plot is for polarized DIS experiments, and the right corresponds to the unpolarized DIS experiments.
• Figure 3: Deeply-inelastic lepton-nucleon scattering mediated by virtual photon exchange.
• Figure 4: The plot on the left shows the world data on $F_2$ as a function of $Q^2$ for fixed values of $x$. On the right we show the converse: $F_2$ as a function of $x$ for fixed values of $Q^2$. From rizvi.
• Figure 5: The valence (up and down) quark, sea quark and gluon distributions plotted as a function of $x$ for fixed $Q^2=10$ GeV$^2$. Note that the sea and glue distributions are scaled down by a factor of $1/20$. From rizvi.