Suppression of Forward Pion Correlations in d+Au Interactions at STAR

Abstract

During the 2008 run RHIC provided high luminosity in both p+p and d+Au collisions at $\sqrt{s_{NN}}=200GeV$. Electromagnetic calorimeter acceptance in STAR was enhanced by the new Forward Meson Spectrometer (FMS), and is now almost contiguous from $-1<\eta<4$ over the full azimuth. This large acceptance provides sensitivity to the gluon density in the nucleus down to $x\approx 10^{-3}$. Measurements of the azimuthal correlation between a forward $\pi^0$ and an associated particle at large rapidity are sensitive to the low-$x$ gluon density. Data exhibit the qualitative features expected from gluon saturation. A comparison to calculations using the Color Glass Condensate (CGC) model is presented.