J/$\psi$ production in ultra-peripheral proton-lead and lead-lead collisions with CMS

This thesis reports on photoproduction of exclusive J/ψ mesons in ultra-peripheral PbPb and pPb collisions at √sNN = 2.76 TeV, and 5.02 TeV, respectively, from the CMS experiment at the LHC. For PbPb collisions, there is a correlation between the directions of the produced J/ψ and the neutron emitted by the struck nucleus. For J/ψ mesons with pT > 100 MeV/c, the ratio of the pT distributions for J/ψ is moving in the opposite direction as the neutrons emitted from the target nucleus to those for J/ψ is moving in the same direction as the neutrons, suggests significant shadowing in the lead nucleus. For pPb collisions, the distributions of the J/ψs in transverse momentum have a sim- ilar form to previous measurements at HERA. The average pT increases with the photon-proton center of mass energy W . This implies that the spatial distribution of the gluons within the proton depends upon the gluon momentum. The cross section also increases as W increases from 57 to 439 GeV implying that the proton become more and more opaque to photons as the photon energy increases. Parametrizing the growth of the cross section by the form σ(W)∝W$^{\delta}$ yields a value of δ =0.636±0.063. This result is consistent with the world average and has a precision comparable to other experiments.