Gluon-Spin Contribution to the Proton Spin from the Double-Helicity Asymmetry in Inclusive π0 Production in Polarized p+p Collisions at s=200GeV

A. Adare et al. (PHENIX Collaboration)
Phys. Rev. Lett. 103, 012003 – Published 1 July 2009

Abstract

The double helicity asymmetry in neutral pion production for pT=1 to 12GeV/c was measured with the PHENIX experiment to access the gluon-spin contribution, ΔG, to the proton spin. Measured asymmetries are consistent with zero, and at a theory scale of μ2=4GeV2 a next to leading order QCD analysis gives ΔG[0.02,0.3]=0.2, with a constraint of 0.7<ΔG[0.02,0.3]<0.5 at Δχ2=9 (3σ) for the sampled gluon momentum fraction (x) range, 0.02 to 0.3. The results are obtained using predictions for the measured asymmetries generated from four representative fits to polarized deep inelastic scattering data. We also consider the dependence of the ΔG constraint on the choice of the theoretical scale, a dominant uncertainty in these predictions.

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  • Received 6 October 2008

DOI:https://doi.org/10.1103/PhysRevLett.103.012003

©2009 American Physical Society

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Vol. 103, Iss. 1 — 3 July 2009

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