Quarkonium production in p-A collisions

Quarkonium production provides a sensitive window for the study of the gluon structure of nucleons and its modification in nuclei. It also provides a very important means of studying the hot-dense conditions created in high-energy collisions of heavy nuclei and a critical probe to look for deconfinement in this hot-dense matter. I review, from an experimental point of view, the physics issues as seen in current experimental results for quarkonium production and try to point out the remaining puzzles and how future measurements, along with more theoretical work, can resolve those puzzles. I discuss production issues including the predicted, but un-observed, J/ψ polarization. Then I show results from fixed target experiments and discuss cold nuclear matter effects including gluon shadowing, parton energy loss and transverse momentum broadening, and final-state absorption of bound states of heavy quarks (c anti c, b anti b). In addition, I highlight the importance of understanding all these effects in cold nuclear matter as a baseline for the search for deconfinement. (orig.)