ALICE results on vector meson photoproduction in ultra-peripheral p-Pb and Pb-Pb collisions

Lead nuclei, accelerated at the LHC, are sources of strong electromagnetic fields that can be used to measure photon-induced interactions in a new kinematic regime. These interactions can be studied in ultra-peripheral p-Pb and Pb-Pb collisions where impact parameters are larger than the sum of the nuclear radii and hadronic interactions are strongly suppressed. Heavy quarkonium photoproduction is of particular interest since it is sensitive to the gluon distribution in the target. The ALICE Collaboration has studied J/psi and psi(2S) photoproduction in ultra-peripheral Pb-Pb collisions and exclusive J/psi photoproduction off protons in ultra-peripheral p-Pb collisions at the LHC. Implications for the study of gluon density distributions and nuclear gluon shadowing are discussed. Recent ALICE results on rho photoproduction are also presented.