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

TL;DR

This paper reports measurements of double helicity asymmetries in forward neutral pion production from polarized proton-proton collisions at 510 GeV, providing insights into gluon polarization at low momentum fractions.

Contribution

It presents new measurements of $A_{LL}$ in the forward region at 510 GeV, extending previous studies and enhancing understanding of gluon polarization at low $x$.

Findings

Measured $A_{LL}$ in forward $ ext{pi}^0$ production at 510 GeV.

Provides data sensitive to low-$x$ gluons.

Complemented previous midrapidity results.

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.