## Rapidity and momentum transfer distributions of coherent J/ψ photoproduction in ultraperipheral pPb collisions at the LHC    [PDF]

V. Guzey, M. Zhalov
Based on accurate calculations of the flux of equivalent photons of the proton and a heavy nucleus and the pQCD framework for the gluon distribution in the proton and nuclei, we analyze the rapidity and momentum transfer distributions of coherent J/{\psi} photoproduction in ultraperipheral proton-Pb collisions at the LHC. We demonstrate that unlike the case of proton-proton UPCs marred by theoretical uncertainties and experimental limitations, after a cut excluding the region of small momentum transfers, ultraperipheral proton-Pb collisions offer a clean way to study the gluon distribution in the proton down to $x \approx 10^{-5}$. Our analysis of the momentum transfer distributions shows that an interplay of J/{\psi} production by low-energy photons on the nucleus and by high-energy photons on the proton in proton-Pb UPCs can result in some excess of events at small $p_t$ in a definite region of the rapidity y.
View original: http://arxiv.org/abs/1307.6689