Gluon-Spin Contribution to the Proton Spin from the Double-Helicity Asymmetry in Inclusive pi(0) Production in Polarized p plus p Collisions at s = 200 GeV
- University of Colorado, Boulder
- ORNL
- Lawrence Livermore National Laboratory (LLNL)
- University of Tennessee, Knoxville (UTK)
The double helicity asymmetry in neutral pion production for p{sub T} = 1 to 12 GeV/c was measured with the PHENIX experiment 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}{sup 2} = 4 GeV{sup 2} a next to leading order QCD analysis gives {Delta}G{sup [0.02,0.3]} = 0.2, with a constraint of -0.7 < {Delta}G{sup [0.02,0.3]} < 0.5 at {Delta}{chi}{sup 2} = 9 (-3{sigma}) 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 {Delta}G constraint on the choice of the theoretical scale, a dominant uncertainty in these predictions.
- Research Organization:
- Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC)
- DOE Contract Number:
- DE-AC05-00OR22725
- OSTI ID:
- 989114
- Journal Information:
- Physical Review Letters, Vol. 103, Issue 1; ISSN 0031-9007
- Country of Publication:
- United States
- Language:
- English
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