Two-particle correlations at forward rapidity in STAR

During the 2008 run RHIC provided high luminosity in both p + p and d + Au collisions at root(S)NN = 200 GeV. Electromagnetic calorimeter acceptance in STAR was enhanced by the new Forward Meson Spectrometer (FMS), and is now almost continuous over -1 < eta < 4 and the full azimuth. This large acceptance provides sensitivity to the gluon density in the nucleus down to x approximate to 10(-3), as expected for 2 -> 2 parton scattering. 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. (C) 2011 Elsevier B.V. All rights reserved.