Double Helicity Asymmetry in \(\pi^{0}\) Production at Midrapidity in Polarized \(p+p\) Collisions at \(\sqrt{s}=510\) GeV

Abstract

PHENIX measurements are presented for the cross-section and double-helicity asymmetry (\(A_{LL}\)) of inclusive \(\pi^{0}\) production (\(A_{LL}^{\pi^{0}}\)) at midrapidity from \(p+p\) collisions at \(\sqrt{s}=510\) GeV from data taken in 2012 and 2013 at the Relativistic Heavy Ion Collider (RHIC). The next-to-leading order (NLO) perturbative QCD (pQCD) calculation agrees excellently with the presented cross-section result. The \(A_{LL}^{\pi^{0}}\) follows an increasingly positive asymmetry as functions of \(p_{T}\) and \(\sqrt{s}\) at the fixed \(x_{T}\). The latest global analysis results, which support the positive spin contribution of gluon (\(\Delta{}G\)), agrees excellently with the presented asymmetry result. The asymmetry result extends the experimental sensitivity to the previously unexplored \(x\) region down to \(x\sim0.01\) and provides additional constraints on \(\Delta{}G\).