Charmonium photoproduction in ultra-peripheral p-Pb and Pb-Pb collisions with ALICE at the LHC

The photoproduction of vector mesons in Ultra-Peripheral Collisions (UPC) is a powerful tool to probe the nuclear gluon distribution (Pb-Pb collisions) and the gluon structure function in the proton (p-Pb collisions). The first measurements of coherent photoproduced J/ψ and ψ(2S) in Pb-Pb collisions at √sNN = 2.76 TeV, performed with the ALICE detector, are described and compared to STARLIGHT and QCD based models, in order to investigate nuclear gluon shadowing. The results of the measurement of exclusive J/ψ photoproduction off protons in p-Pb collisions at √sNN = 5.02 TeV are also presented