Orateur
Description
One of the most intriguing results in ultra-peripheral collisions (UPCs) of heavy ions is that the cross section of J/ψ photoproduction in heavy nuclei has been found to be significantly suppressed relative to that of a free proton. The suppression was found across a wide range of photon-nucleon center-of-mass energy, going from below 20 GeV to nearly 1 TeV. Many theoretical models can describe the data in a specific kinematic regime, while none of the model can describe the entire energy dependence. In this talk, I will present a new idea[1] about utilizing a set of ratio measurements in UPCs by comparing diffractive Vector-Meson production (Pomeron exchange) and inclusive hadron production (single gluon exchange) to exploit their distinct sensitivity to saturation phenomena. This ratio exhibits a unique and measurable signature for gluon saturation, which is expected to be qualitatively different than other models, e.g., leading twist shadowing. Experimental opportunities at the Relativistic Heavy-Ion Collider, the Large Hadron Collider, and the Electron-Ion Collider will be discussed.
[1] Yuri V. Kovchegov, Huachen Sun, Zhoudunming Tu, "Novel Cross Section Ratios as Possible Signals of Saturation in UPCs", arXiv:2311.12208, submitted to PRD
