  The double helicity asymmetry in neutral pion production for p_T = 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 \mu^2 = 4 GeV^2 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-chi^2 = 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.
