The gluon spin contribution to the proton spin from the double helicity asymmetry in inclusive pi0 production in polarized p+p collisions at sqrt(s)=200 GeV
Abstract
The double helicity asymmetry in neutral pion production for pT = 1 to 12 GeV/c has been measured with the PHENIX experiment in order to access the gluon spin contribution, Delta-G, to the proton spin. Measured asymmetries are consistent with zero, and at a theory scale of μ2 = 4 GeV2 give Delta-G[0.02,0.3] = 0.1 to 0.2, with a constraint of -0.7 < Delta-G[0.02,0.3] < 0.5 at Delta-chi2 = 9 (~3 sigma) for our sampled gluon momentum fraction (x) range, 0.02 to 0.3. The results are obtained using predictions for our measured asymmetries generated from four representative fits to polarized deep inelastic scattering data. We also consider the dependence of the Delta-G constraint on the choice of theoretical scale, a dominant uncertainty in these predictions.