Neutral pion cross section and spin asymmetries at intermediate pseudorapidity in polarized proton collisions at root s=200 GeV

Abstract

The differential cross section and spin asymmetries for neutral pions produced within the intermediate pseudorapidity range 0.8 < eta < 2.0 in polarized proton-proton collisions at root s = 200 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 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 approximate to 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 (eta approximate to 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.