The Double Helicity Asymmetry in Neutral Pion Production at PHENIX and Its Constraint on $\Delta G$ Through Global Analysis

Understanding the gluon spin contribution to the proton spin, $\Delta G$, is a primary goal of the RHIC spin program. The abundant production of pions in $p+p$ collisions, coupled with the PHENIX detector's fine resolution Electromagnetic Calorimeter and high $p_T$ triggering capabilities, make neutral pions a prime candidate to study the proton spin structure in polarized $p+p$ collisions at RHIC. Measurements of the double helicity asymmetry, $A_{LL}$, in $\pi^0$ production from 2005 and 2006 were shown to significantly constrain the gluon helicity distribution, $\Delta G$, in the proton [1]. With improved luminosity and polarization, the figure of merit for the 2009 data set was a factor of 1.5 better that the previous runs combined. We present the 2009 results for $\pi^0$ $A_{LL}$, along with a discussion of the results from inclusion of these data in a recent update of the DSSV global analysis.\\[4pt] [1] D. de Florian, R. Sassot, M. Stratmann, W. Vogelsang (DSSV) Phys.Rev.Lett. 101 (2008) 072001