Charged-pion cross sections and double-helicity asymmetries in polarized collisions at GeV

Imai, Kenichi; Tanida, Kiyoshi   ; PHENIX Collaboration*

We present midrapidity charged-pion invariant cross sections, the ratio of the to cross sections and the charge-separated double-spin asymmetries in polarized collisions at GeV. While the cross section measurements are consistent within the errors of next-to-leading-order (NLO) perturbative quantum chromodynamics predictions (pQCD), the same calculations overestimate the ratio of the charged-pion cross sections. This discrepancy arises from the cancellation of the substantial systematic errors associated with the NLO-pQCD predictions in the ratio and highlights the constraints these data will place on flavor-dependent pion fragmentation functions. The charge-separated pion asymmetries presented here sample an range of - and provide unique information on the sign of the gluon-helicity distribution.