  The new forward Muon Piston Calorimeters allow PHENIX to explore low-$x$
parton distributions in d+Au collisions with hopes of observing gluon
saturation. We present a two-particle azimuthal $\Delta \phi$ correlation
measurement made between a mid-rapidity particle ($|\eta_1| < 0.35$) and a
forward $\pi^0$ ($3.1 < \eta_2 < 3.9$) wherein we compare correlation widths in
d+Au to p+p and compute $I_{dA}$.
