Measurement of gluon polarization contribution to proton spin through Charged Pion probes at PHENIX

The RHIC spin program is designed to study the nucleon spin structure. A major research is to determine the gluon contribution to the total proton spin with the use of channels in longitudinally polarized proton-proton collisions. When taken along with other channels (e.g. associated with neutral $\pi^0$ mesons, direct photons and $\eta$ particles) the single inclusive charged pion channel can constrain the contribution of gluon spin, $\Delta G$, additionally it can give the sign information on $\Delta G$. The goal of this analysis is to measure the asymmetry $A_{LL}$ as a function of transverse momentum($p_T$) of charged pion with central arm tracking in PHENIX and eventually to use it along with other data to extract $\Delta G$ using next to leading order pQCD calculation. For this purpose, the kinematic region of interest is $p_T >$ 5GeV/c where quark-gluon and gluon-gluon hard processes dominate charged pion production at midrapidity. The status of the charged pion $A_{LL}$ analysis on the 2009 Run data at center of mass energies of 200GeV with $\sim$55\% polarization and integrated luminosity $\sim$15~pb$^{-1}$ will be presented.