## Exclusive J/ψ production in ultraperipheral collisions at the LHC: constrains on the gluon distributions in the proton and nuclei    [PDF]

V. Guzey, M. Zhalov
Using the framework of collinear factorization in perturbative QCD (pQCD), we analyze the recent data of the LHCb and ALICE collaborations on exclusive photoproduction of J/{\psi} in ultraperipheral pp and AA collisions, respectively. We demonstrate that the simultaneous analysis of the proton and Pb data allows us to reduce the ambiguity of the pQCD description of the $\gamma p \to J/\psi p$ and $\gamma A \to J/\psi p$ cross sections and, hence, to place additional constraints on the gluon distributions in the nucleon and nuclei at small x. We also make predictions for the cross section of coherent exclusive photoproduction of J/{\psi} in nucleus-nucleus ultraperipheral collisions accompanied by the electromagnetic excitation of nuclei and the subsequent neutron emission.
View original: http://arxiv.org/abs/1307.4526