Abstract: How well do we really understand cold nuclear matter?
The measurement of charmonium suppression in relativistic heavy ion
collisions is posited to be an unambiguous probe of the properties of
the strongly interacting quark gluon plasma (sQGP). In hot and dense
QCD matter Debye color screening prevents charm and anti-charm quark
pairs from forming $J/psi$ mesons if the screening radius is smaller
than the binding radius. However, one must have a clear understanding
of the expected suppression in normal density QCD matter before
interpreting any additional anomalous suppression.
The PHENIX experiment has measured $J/psi$ production from colliding
proton+proton and deuteron+gold beams at 200GeV from the relativistic
heavy ion collider (RHIC). The deuteron+gold data can be compared to
the proton+proton baseline in order to establish the typical
suppression in cold nuclear matter. For PHENIX, a suppression of
$J/psi$ in cold nuclear matter is observed as one goes forward in
rapidity (in the deuteron-going direction), corresponding to a region
more sensitive to initial state low-x gluons in the gold
nucleus. These results can be convoluted with the
nuclear-environment-modified parton distribution functions, measured
in DIS, in order to extract the $J/psi$ break up (absorption) cross
section in cold nuclear matter. In this talk I will compare and
contrast the PHENIX results with results obtained at E866, SPS, and
the HERA-B experiments for $J/psi$ suppression. One interesting
question to ask is how well these different data agree with
each-other, or in other words how universal is the $J/psi$
suppression in cold nuclear matter across different colliding systems
and different energies. In addition, projections for future results
using the data acquired by the PHENIX experiment in Run6 (p+p) and
Run8 (d+Au) will be presented. These data, which are in the process of
being analyzed, will provide a needed improvement in the statistical
and systematic precision of constraints for cold nuclear matter (CNM)
effects. These CNM-effect constraints must be improved in order to
make firm conclusions concerning additional hot nuclear matter
charmonium suppression in the sQGP.