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

L. Adamczyk, J. K. Adkins, G. Agakishiev, M. M. Aggarwal, Z. Ahammed, I. Alekseev, J. Alford, C. D. Anson, A. Aparin, D. Arkhipkin, E. C. Aschenauer, G. S. Averichev (+364 others)
2014 Physical Review D  
The differential cross section and spin asymmetries for neutral pions produced within the intermediate pseudorapidity range 0.8 < η < 2.0 in polarized proton-proton collisions at sqrts = 200 GeV are presented. Neutral pions were detected using the endcap 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 be within the scale uncertainty of a next-to-leading order perturbative QCD
more » ... on. The longitudinal double-spin asymmetry, A_LL, is measured in the same pseudorapidity range. This quantity is sensitive to the gluonic contribution to the proton spin, Δg(x), at low Bjorken-x (down to x approx 0.01), where it is less constrained by measurements at central pseudorapidity. The measured A_LL is consistent with model predictions. 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 within a previously unexplored kinematic range in Feynman-x and p_T. Such measurements may aid our understanding of the on-set and kinematic dependence of the large asymmetries observed at more forward pseudorapidity (η approx 3) and their underlying mechanisms. The A_N results presented are consistent with a twist-3 model prediction of a small asymmetry within the present kinematic range.
doi:10.1103/physrevd.89.012001 fatcat:rydahzu6yrdqdj4jjnwkke7b4m