Inclusive cross section and double helicity asymmetry for π^0 production in p+p collisions at sqrt(s)=200 GeV: Implications for the polarized gluon distribution in the proton

Abstract

The PHENIX experiment presents results from the RHIC 2005 run with polarized proton collisions at sqrt(s)=200 GeV, for inclusive π^0 production at mid-rapidity. Unpolarized cross section results are given for transverse momenta p_T=0.5 to 20 GeV/c, extending the range of published data to both lower and higher p_T. The cross section is described well for p_T < 1 GeV/c by an exponential in p_T, and, for p_T > 2 GeV/c, by perturbative QCD. Double helicity asymmetries A_LL are presented based on a factor of five improvement in uncertainties as compared to previously published results, due to both an improved beam polarization of 50%, and to higher integrated luminosity. These measurements are sensitive to the gluon polarization in the proton, and exclude maximal values for the gluon polarization.

375 authors, 7 pages, 3 figures. Submitted to Phys. Rev. D, Rapid Communications. Plain text data tables for the points plotted in figures for this and previous PHENIX publications are (or will be) publicly available at http://www.phenix.bnl.gov/papers.html

References in corpus (7)

• Centrality Dependence of pi^0 and eta Production at Large Transverse Momentum in sqrt(s_NN) = 200 GeV d+Au Collisions
• Longitudinal double-spin asymmetry and cross section for inclusive jet production in polarized proton collisions at sqrt(s) = 200 GeV
• Measurement of direct photon production in p + p collisions at sqrt(s) = 200 GeV
• Nuclear Effects on Hadron Production in d+Au and p+p Collisions at sqrt(s_NN)=200 GeV
• Jet Properties from Dihadron Correlations in p+p Collisions at sqrt(s)=200 GeV
• Single Transverse-Spin Asymmetry in Very Forward and Very Backward Neutral Particle Production for Polarized Proton Collisions at sqrt{s} = 200 GeV
• Improved Measurement of Double Helicity Asymmetry in Inclusive Midrapidity pi^0 Production for Polarized p+p Collisions at sqrt(s)=200 GeV

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