Spin Effects in Forward pi^0-production in Polarized Proton-Proton Collisions at STAR

TL;DR

This paper investigates spin asymmetries in forward pi^0 production during polarized proton collisions at 200 GeV, finding asymmetries increase with x_F and align with phenomenological models, while cross sections match pQCD predictions.

Contribution

It presents new measurements of single spin asymmetries in forward pi^0 production at STAR, supporting models involving the Sivers, Collins, and twist-3 effects.

Findings

Asymmetry is zero for negative x_F.

Asymmetry increases with positive x_F.

Cross sections agree with pQCD calculations.

Abstract

We report some results in large pseudo rapidity pi^0-production in polarized proton collisions at 200 GeV center of mass energy. The single spin asymmetry for positive Feynman x (x_F) is consistent with zero up to ~0.35, then increases with increasing x_F. This behavior can be described by phenomenological models including the Sivers effect, Collins effect or twist-3 contributions in initial and final states. The asymmetry is found to be zero for negative x_F (-0.6<x_F<-0.2). It has been observed that inclusive p+p->pi^0+X cross sections at \eta=3.3, 3.8 and 4.0 are consistent with next-to-leading order perturbative QCD calculations.