Imprints of nuclear shell structure in exclusive vector meson production

Abstract

We report for the first time that, within the saturation framework, exclusive vector meson production at small $x$ is sensitive to the shell structure of the target nucleus. Self-consistent nuclear densities from occupied single-particle orbitals in the quark-meson coupling (QMC) model modify the coherent $|t|$-differential cross section, enhancing the secondary diffractive lobes for light nuclei and displacing the higher-order minima in $|t|$ for intermediate-mass nuclei, whereas for heavy targets the shifts are weaker and appear at larger $|t|$. Because the small $J/\psi$ dipole is insensitive to saturation, these features make coherent $J/\psi$ production a clean probe of nuclear shell structure, most favorably for intermediate-mass nuclei such as the calcium isotopes. For the larger $\varphi$ dipole, shell structure must be included in the nuclear initial state before saturation effects can be isolated in differential observables at the EIC. Our results establish exclusive vector meson production as a probe of the mean-field, single-particle structure of nuclei at small $x$, and provide a baseline for isolating residual many-body correlations.