Seminar in Hadronic Physics

Probing gluon saturation and nuclear structure in photon-nucleus collisions

Heikki Mantysaari

Jyvaskyla University

Ultra peripheral heavy ion collisions measured at RHIC and at the LHC provide a unique opportunity to study photon-nucleus scattering in the very high center-of-mass energy domain. Exclusive vector meson photoproduction is an especially interesting process in UPCs as it is experimentally clean, and additionally such diffractive processes are especially sensitive to non-linear QCD dynamics.

We calculate exclusive J/Psi production in the dipole picture, describing the interaction with the dense target in the Color Glass Condensate framework. The energy dependence of the target structure (or the cross section) is obtained by solving the perturbative JIMWLK evolution equation. We predict a strong saturation-driven nuclear suppression at high energies, while the LHC data (that is currently available up to ~1TeV center-of-mass energies) prefers even stronger suppression, and determine the effect of nucleon shape fluctuations on the nuclear suppression in the coherent and incoherent cross sections. Additionally we explore possibilities to use more differential exclusive vector meson production measurements to probe the nuclear structure. In particular, we study p_T dependence of the cross section to probe saturation effects on the nuclear geometry, and azimuthal asymmetries in the decay product distribution to probe nuclear deformations. We furthermore explore the possibilities to probe the spatial distribution of small-x gluon field in a polarized deuteron at the EIC.