Cold Nuclear Matter Effects on J/ψ and Υ Production at the 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 Υ(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 Υ(1S), scale less than linearly with the number of binary nucleon-nucleon collisions. 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. We characterize these effects and study their energy and rapidity dependence.