Sprecher
Beschreibung
Ultra-peripheral collisions (UPCs) of light nuclei provide a unique opportunity to investigate both the spatial structure of nuclei and the dynamics of gluons at small Bjorken-$x$. In this contribution, I will present predictions for exclusive $\mathrm{J}/\psi$ photoproduction in oxygen-oxygen and neon-neon UPCs within an impact-parameter-dependent Color Glass Condensate framework incorporating JIMWLK evolution. The model is constrained by a recent global Bayesian analysis [1] of proton and lead photoproduction data, enabling theoretical uncertainties to be systematically propagated to predictions for light-ion collisions.
Particular emphasis is placed on the sensitivity of diffractive observables to the underlying nuclear structure. I will compare state-of-the-art descriptions of oxygen and neon nuclei, including PGCM, NLEFT, and VMC calculations, and demonstrate that while integrated cross sections depend only weakly on the nuclear wave function, the momentum-transfer dependence of coherent and incoherent vector meson production retains measurable information on the nuclear geometry. In particular, the ratio of diffractive cross sections for neon and oxygen emerges as a promising observable to discriminate between different nuclear structure models while reducing theoretical uncertainties [2].
I will also discuss how UPC measurements with light nuclei can probe the onset of gluon saturation by systematically exploring the nuclear mass-number dependence of saturation effects [2]. These results highlight the strong potential of future LHC light-ion runs, together with measurements at the Electron-Ion Collider, to simultaneously constrain nuclear structure and the small-$x$ dynamics of QCD.
[1] Mantysaari, H., Roch, H., Salazar, F., Schenke, B., Shen, C., & Zhao, W. (2026). Global Bayesian analysis of J/ψ photoproduction on proton and lead targets. Phys. Rev. D, 113(1), 014038. https://doi.org/10.1103/pcmz-dyz1
[2] Mantysaari, H., Roch, H., Schenke, B., Shen, C., & Zhao, W. (2026). Nuclear structure and saturation effects from diffractive vector meson production. arXiv preprint arXiv:2605.00454. https://doi.org/10.48550/arXiv.2605.00454