Neutral pion cross section and spin asymmetries at intermediate pseudorapidity in polarized proton collisions ats=200 GeV
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Abstract
The differential cross section and spin asymmetries for neutral pions produced within the intermediate pseudorapidity range $0.8<\ensuremath{\eta}<2.0$ in polarized proton-proton collisions at $\sqrt{s}=200\text{ }\text{ }\mathrm{GeV}$ are presented. Neutral pions were detected using the end cap electromagnetic calorimeter in the STAR detector at RHIC. The cross section was measured over a transverse momentum range of $5<{p}_{T}<16\text{ }\text{ }\mathrm{GeV}/c$ and is found to agree with a next-to-leading order perturbative QCD calculation. The longitudinal double-spin asymmetry ${A}_{LL}$ is measured in the same pseudorapidity range and spans a range of Bjorken-$x$ down to $x\ensuremath{\approx}0.01$. The measured ${A}_{LL}$ is consistent with model predictions for varying degrees of gluon polarization. The parity-violating asymmetry ${A}_{L}$ is also measured and found to be consistent with zero. The transverse single-spin asymmetry ${A}_{N}$ is measured over a previously unexplored kinematic range in Feynman-$x$ and ${p}_{T}$. Such measurements may aid our understanding of the onset and kinematic dependence of the large asymmetries observed at more forward pseudorapidity ($\ensuremath{\eta}\ensuremath{\approx}3$) and their underlying mechanisms. The ${A}_{N}$ results presented are consistent with a twist-3 model prediction of a small asymmetry over the present kinematic range.
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