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

摘要

Vector mesons are copiously produced in ultra-peripheral collisions. In thesecollisions, the impact parameter is larger than the sum of the radii of twoprojectiles, implying that electromagnetic processes become dominant. The crosssection for this process is sensitive to the gluon distribution and cantherefore probe nuclear gluon shadowing (Pb-Pb) and the gluon structurefunction in the nucleon (p-Pb). The ALICE Collaboration has performed the firstmeasurement of the coherent J/$\psi$ and $\psi$(2S) photoproduction crosssection in Pb-Pb collisions and that for exclusive J/$\psi$ photoproduction offprotons in ultra-peripheral proton-lead collisions at the LHC. The results arecompared to STARLIGHT and to QCD based models.