Speaker
Description
Diffractive vector meson production provides a powerful probe of gluon saturation and the spatial structure of small-x gluons. Within the Color Glass Condensate (CGC) framework, it is sensitive to both nonlinear dynamics and event-by-event fluctuations in the proton wave function. HERA data, particularly for ${J/\psi}$ photoproduction, suggest that the gluonic radius of the proton is smaller than its charge radius.
We introduce a model for the spatial structure of the proton where the gluonic hot spots are distributed along Y-shaped color flux tubes, simultaneously reproducing charge and gluonic radii. The model is implemented in an impact-parameter-dependent McLerran–Venugopalan framework with JIMWLK evolution.
A combined Bayesian analysis of HERA and LHC ultraperipheral collision data shows that, while proton data are well described, nuclear cross sections are overestimated at high energies, indicating insufficient saturation effects. This tension can be mitigated by introducing an overall normalization factor that accounts for model uncertainties.
We present predictions for nuclear targets and show that both correlation observables and momentum-transfer-dependent cross-section ratios provide sensitive probes of proton geometry and can discriminate between different models in future measurements.
Finally we demonstrate how future ${\gamma}$+O and ${\gamma}$+Ne studies at the LHC or at the EIC can probe the structure of the light nuclei.
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