  One of the fundamental goals of the PHENIX experiment is to understand the
structure of cold nuclear matter, since this serves as the initial state for
heavy-ion collisions. Knowing the initial state is vital for interpreting
measurements from heavy-ion collisions. Moreover, the structure of the cold
nucleus by itself is interesting since it is a test-bed for our understanding
of QCD. In particular there is the possibility of novel QCD effects such as
gluon saturation at low-x in the nucleus. At RHIC we can probe the behavior of
gluons at low-x by measuring the pair cross-section of di-hadrons from di-jets
in d+Au collisions. Our results show a systematic decrease in the pair
cross-section as one goes to smaller impact parameters of the nucleus, and also
as one goes to lower Bjorken x. There is a possibility that these interesting
effects come from gluon recombination at low x in the Au nucleus.
