Double Helicity Asymmetries of Forward Neutral Pions from $\sqrt{s}=510$ GeV $pp$ Collisions at STAR

Abstract

Longitudinally polarized $p+p$ scattering experiments provide access to gluon polarization via measurement of the double helicity asymmetry, $A_{LL}$. At the completion of the 2013 RHIC running period, a significant dataset of ${\pi }^0$s corresponding to an integrated luminosity of 46 ${\text{pb}}^{-1}$ (2012) and 8 ${\text{pb}}^{-1}$ (2013) produced from polarized $p+p$ scattering at $\sqrt{s}=510$ GeV with an average beam polarization of approximately $50\%$ was acquired. The ${\pi }^0$ kinematics were measured via isolation cones by the STAR Forward Meson Spectrometer, an electromagnetic calorimeter covering a forward pseudorapidity range of $2.6<\eta <4$. The asymmetric $qg\to qg$ subprocess becomes more dominant in this forward region than in the midrapidity region; furthermore, asymmetry measurements in the forward region are sensitive to low-$x$ gluons. Progress on $A_{LL}$ determined from forward ${\pi }^0$ events, complementing previous midrapidity measurements, are presented.

SPIN2014 Proceeding

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