Gluon-Spin Contribution to the Proton Spin from the Double-Helicity Asymmetry in Inclusive pi⁰ Production in Polarized p + p Collisions s = 200 GeV

Journal Article · Thu Jan 01 04:00:00 EST 2009 · Physical Review Letters

DOI:https://doi.org/10.1103/PhysRevLett.103.012003· OSTI ID:961564

Adare, A. ^[1]; Awes, Terry C ^[2]; Cianciolo, Vince ^[2]; Enokizono, Akitomo ^[3]; Read, Jr, Kenneth F ^[2]; Silvermyr, David O ^[2]; Sorensen, Soren P ^[4]; Stankus, Paul W ^[2]; Young, Glenn R ^[2]

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1. University of Colorado, Boulder
2. ORNL
3. Oak Ridge National Laboratory (ORNL)
4. 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 ({approx}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 Laboratory (ORNL)
• Sponsoring Organization: SC USDOE - Office of Science (SC)
• DOE Contract Number: AC05-00OR22725
• OSTI ID: 961564
• Journal Information: Physical Review Letters, Journal Name: Physical Review Letters Journal Issue: 1 Vol. 103; ISSN 0031-9007; ISSN PRLTAO
• Country of Publication: United States
• Language: English

Related Subjects

71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
ASYMMETRY
DEEP INELASTIC SCATTERING
GLUONS
HELICITY
PIONS
PRODUCTION
PROTONS
QUANTUM CHROMODYNAMICS
SPIN