Forward Neutral Pion Production inp+pandd+AuCollisions atsNN=200 GeV

Measurements of the production of forward ${\ensuremath{\pi}}^{0}$ mesons from $p+p$ and $d+\mathrm{Au}$ collisions at $\sqrt{{s}_{NN}}=200\text{ }\text{ }\mathrm{GeV}$ are reported. The $p+p$ yield generally agrees with next-to-leading order perturbative QCD calculations. The $d+\mathrm{Au}$ yield per binary collision is suppressed as $\ensuremath{\eta}$ increases, decreasing to $\ensuremath{\sim}30%$ of the $p+p$ yield at $⟨\ensuremath{\eta}⟩=4.00$, well below shadowing expectations. Exploratory measurements of azimuthal correlations of the forward ${\ensuremath{\pi}}^{0}$ with charged hadrons at $\ensuremath{\eta}\ensuremath{\approx}0$ show a recoil peak in $p+p$ that is suppressed in $d+\mathrm{Au}$ at low pion energy. These observations are qualitatively consistent with a saturation picture of the low-$x$ gluon structure of heavy nuclei.