2025 EIC-France Workshop: Physics Highlights and Perspectives

Abstract

This document presents a synthesis of the theory contributions and discussions from the 2nd EIC-France Workshop, held at IJCLab (Orsay) on 1-3 December 2025. The workshop brought together members of the French hadron-physics community to review recent theoretical developments relevant to the future Electron-Ion Collider (EIC) and to coordinate national efforts in preparation for its early physics program. The report first summarizes the collider's initial running conditions and luminosity performance, as outlined in the EIC Early Science Matrix. It then provides concise overviews of the theoretical presentations on inclusive, semi-inclusive, exclusive, heavy-flavor, and small-x physics. Based on these discussions, two measurements emerged as especially well suited for early EIC operation and strongly aligned with areas of established French expertise: inclusive diffraction and inclusive quarkonium production. These channels offer clean signatures, robust theoretical interpretability, and direct sensitivity to fundamental QCD phenomena such as gluon saturation, heavy-quark dynamics, and the small-x structure of hadrons and nuclei. In addition, the workshop identified longer-term physics opportunities that will benefit from the full capabilities of the EIC after its ramp-up phase. These include accessing the three-dimensional structure of the pion through the Sullivan process and a broader program of exclusive three-body final states, both of which represent high-impact avenues for exploring hadronic structure and non-perturbative QCD. Together, the elements summarized in this report provide a coherent overview of the strategic priorities and scientific ambitions shaping the French community's contribution to the EIC physics program.

Figures (6)

• Figure 1: Left: the ratio $F_{2,A}^{D}/(AF_{2,p}^{D})$ of the diffractive structure functions as a function of $\beta=Q^2/(Q^2+M_X^2)$ for Ca, Sn and Au nuclei ($M_X$ being the invariant mass of the diffractively produced system); results are for the "non breakup" case, at $Q^2=5\ \hbox{GeV}^2$ and $x_{\mathbb P}=x/\beta=0.001$. Right: the same ratio for Au nuclei and transversely or longitudinally polarized virtual photon; both "breakup" and "non breakup" cases are compared as a function of $Q^2$ for $x_{\mathbb P}=x/\beta=0.001.$
• Figure 2: $P_T$-differential inclusive prompt photoproduction cross sections for (a) single $J/\psi$ and (b) for $J/\psi$ in association with charm. Figure from Ref. Flore:2020jau.
• Figure 3: Diagrammatic representation of the Sullivan DVCS process.
• Figure 4: Number of events and beam spin asymmetries expected at the EIC. Blue crosses: pure Bethe-Heitler contribution. Open black squares : CSM-based pion GPD-model Chavez:2021llq without gluon-GPDs. Filled black squares: complete CSM-based model including gluons and its uncertainty (gray band). Filled red dots : GRS-based model Gluck:1999xe including gluons. Figure from Ref. Chavez:2021koz.
• Figure 5: Diagrammatic representation of the exclusive process with the production of a pair of mesons, illustrated by the case of a $\rho$-meson pair. Left: production of a $\rho_L-\rho_L$ pair, giving access to chiral-even quark GPDs at leading twist. Right: production of a $\rho_L-\rho_T$ pair, giving access to chiral-odd quark GPDs at leading twist.