Journal
PHYSICAL REVIEW LETTERS
Volume 103, Issue 1, Pages -Publisher
AMER PHYSICAL SOC
DOI: 10.1103/PhysRevLett.103.012003
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Funding
- Office of Nuclear Physics
- NSF
- Renaissance Technologies (U.S.)
- MEXT and JSPS (Japan)
- CNPq and FAPESP (Brazil)
- NSFC (China)
- MSMT (Czech Republic)
- IN2P3/CNRS and CEA (France)
- BMBF, DAAD, and AvH (Germany)
- OTKA (Hungary)
- DAE (India)
- ISF (Israel)
- KRF and KOSEF (Korea)
- MES, RAS, and FAAE (Russia)
- U. S. CRDF for the FSU
- U.S.-Hungary Fulbright
- U.S.-Israel BSF
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The double helicity asymmetry in neutral pion production for p(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 2 = 4 GeV2 a next to leading order QCD analysis gives Delta G([0.02,0.3]) = 0.2, with a constraint of -0.7 < Delta G([0.02,0.3]) < 0.5 at Delta chi(2) = 9 (similar to 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.
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