Heavy Ion Tea

Measurement of the Double Helicity Asymmetry in Neutral Pion
Production in Polarized Proton Collisions at PHENIX and its
Impact on the Gluon Spin Contribution to the Proton Spin

Kieran Boyle(SUNY Stony Brook)

Abstract: Results from polarized DIS experiments have shown that the spin of quarks accounts for only a small fraction of the total proton spin. A primary goal of the RHIC Spin program is to measure the gluon spin contribution DeltaG to the spin of the proton through the measurement of double helicity asymmetries A_LL in polarized proton collisions. Pions are abundantly produced in proton-proton collisions and so are a good candidate for a high statistics analysis. The PHENIX EMCal has good energy resolution and high granularity which, when used with a high energy photon trigger, yield a substantial pi0 sample over a wide range in transverse momentum (p_T). The 2005 and 2006 polarized proton runs (at 200 GeV center of mass energy) saw large increases in luminosity (L) and polarization (P) compared to previous runs, resulting in a high figure of merit (P^4 L). pi0 A_LL from 2005 and 2006 are precise enough to be sensitive to DeltaG. Results from 2005 and 2006 for pi0 A_LL at mid rapidity will be shown and their impact on DeltaG will be discussed.