Recent STAR Results from Charged Pion Production in Polarized pp Collisions at $\sqrt{s} = 200 GeV$ at RHIC

Abstract

The STAR experiment at RHIC measures the longitudinal double-spin asymmetry $A_{LL}$ for a variety of final states in collisions of longitudinally polarized protons to constrain the polarized gluon distribution in the proton. Asymmetries for mid-rapidity charged pion production benefit from large cross-sections and the excellent tracking and particle identification capabilities of the STAR Time Projection Chamber. This contribution presents a measurement of the ratio of cross sections for inclusive $\pi^{-}$ and $\pi^{+}$ production using data collected in 2005, as well as a new measurement of $A_{LL}$ for charged pions opposite a jet obtained from the 2006 RHIC run.