Speaker
Description
In ultraperipheral heavy-ion collisions (UPCs), vector meson photoproduction, e.g. $\rho^{0}$ and $J/\psi$, has been considered one of the most sensitive probes for studying the gluonic structure in heavy nuclei. The linear polarization of the photons involved enables detailed imaging of the nucleus through spin interference effects. Recently, extensive efforts by the STAR experiment at RHIC and the ALICE experiment at the LHC have significantly advanced our understanding of both coherent and incoherent vector meson photoproduction, nuclear gluon shadowing, and quantum interference phenomena in UPCs.
In this talk, we present the latest differential cross-section measurements of coherent and incoherent $J/\psi$ photoproduction in Au+Au, Ru+Ru, and Zr+Zr UPCs at $\sqrt{s_{_\mathrm{NN}}} = 200$ GeV from STAR, with a focus on angular modulations arising from spin interference. We also highlight recent ALICE results on $\rho^{0}$ and $J/\psi$ photoproduction in Pb+Pb UPCs at $\sqrt{s{_\mathrm{NN}}} = 5.02$ TeV. Comparisons between STAR and ALICE data provide crucial insights into the energy and Bjorken-$x$ dependence of nuclear gluon distributions and the emergence of gluon saturation effects. These results offer new constraints on nuclear parton distribution functions and sub-nucleonic spatial fluctuations. The talk will conclude with an outlook on future UPC opportunities at RHIC, the forthcoming LHC Run 4, and related physics prospects at the upcoming Electron-Ion Collider.
