Two-particle azimuthal correlations at forward rapidity in STAR
During the 2008 run the Relativistic Heavy Ion Collider (RHIC) at the Brookhaven Nation Laboratiory (BNL), NY, provided high luminosity in both p+p and d+Au collisions at $\sqrt{s_{NN}}=200\mathrm{\,GeV}$. Electromagnetic calorimeter acceptance in STAR was enhanced by the new Forward Meson Spectrometer (FMS), and is now almost contiguous from $-1<η\4$ over the full azimuth. This allows measurements of the azimuthal correlation between a forward neutral pion and a second particle in a very large rapidity range. Di-hadron azimuthal correlations provide sensitivity to the low longitudinal momentum fraction ($x$) component of the gluon density in the nuclear target. Initial state nonlinear effects are in fact expected to appear in d+Au collisions when the dense part of the nucleus is probed. The analysis in this thesis shows that such correlations and their dependence on rapidity, transverse momentum and collision centrality are qualitative consistent with the existence of gluon saturation effects in the relativistic nucleus. Theoretical expectations for azimuthal correlations between a dilute system (deuteron) and a saturated target (Gold nucleus) have been explored.