Probing the Low-x Structure of the Nucleus with the PHENIX Detector

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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.