The Double-Longitudinal Spin Asymmetry in Charged Pion Production at PHENIX: Determining the Sign of $\Delta g$

The Relativistic Heavy Ion Collider (RHIC) began colliding polarized protons in 2001. Early measurements of the double- longitudinal asymmetry ($A_{LL}$) in the production of neutral pions, sensitive to $\Delta g$, the gluon's contribution to the spin of the proton, have been performed by the PHENIX experiment. Because a significant fraction of pion production in the presently accessible kinematic region is due to gluon-gluon scattering, the factorized polarized cross section contains $\Delta g$ twice, and thus the current measurement is not sensitive to the sign of the gluon contribution. Pion production at higher transverse momentum ($p_T$) will be dominated instead by quark-gluon scattering. The difference between $A_{LL}$ of positive and negative pions at high $p_T$ will be particularly sensitive to the sign of $\Delta g$. The current status of the charged pion $A_{LL}$ analysis using PHENIX data from the 2003 and 2004 polarized proton runs at RHIC will be presented.