UC Riverside

The Quark-Gluon Plasma (QGP), a new hot dense matter created by melting the protons and neutrons in nucleus, was discovered at RHIC (Relativistic Heavy Ion Collider). The Universe passed through a QGP stage about 10 µs after the Big Bang before condensing into the familiar particles - primarily protons or neutrons. Experiments have shown thatthe QGP behaves like a strongly coupled liquid instead of a weakly couple gas - which was the original expectation. One key to understanding the QGP is the initial state. Experiments at HERA (Hadron Electron Ring Accelerator) suggest that protons and neutrons are dominated by gluons if we probe at small x (longitudinal momentum fraction). This effect should be more substantial in nuclei due to the large number of nucleons. One theory called Color Glass Condensate (CGC) proposed the gluon is saturated in nuclei if we probe below the saturation scale. We can use a dilute system (deuteron) to probe a dense system (gold) to investigate the saturation. Experiments have seen signs of saturation in the d+Au collisions, though these effects are subject to interpretation. In this thesis, using the MPCEX (Muon Piston Calorimeter Extension) in the PHENIX experiment at RHIC, I explore saturation effects in d+Au collision in the forward direction and present the suppression of neutral pions.