Cold nuclear matter effects on J/ψ and Γ production at energies available at the CERN Large Hadron Collider (LHC)

The charmonium yields are expected to be considerably suppressed if a deconfined medium is formed in high-energy heavy-ion collisions. In addition, the bottomonium states, with the possible exception of the Gamma(1S) state, are also expected to be suppressed in heavy-ion collisions. However, in proton-nucleus collisions the quarkonium production cross sections, even those of the Gamma(1S), are also suppressed. These "cold nuclear matter" effects need to be accounted for before signals of the high-density QCD medium can be identified in the measurements made in nucleus-nucleus collisions. We identify two cold nuclear matter effects important for midrapidity quarkonium production: "nuclear absorption," typically characterized as a final-state effect on the produced quarkonium state, and "shadowing," the modification of the parton densities in nuclei relative to the nucleon, an initial-state effect. In this article, we characterize these effects and study the energy, rapidity, and impact-parameter dependence of initial-state shadowing.