Inclusive double-helicity asymmetries in neutral pion and eta meson production in $\vec{p}+\vec{p}$ collisions at $\sqrt{s}=200$ GeV

Abstract

Results are presented from data recorded in 2009 by the PHENIX experiment at the Relativistic Heavy Ion Collider for the double-longitudinal spin asymmetry, $A_{LL}$, for ${\pi }^0$ and $\eta$ production in $\sqrt{s}=200$ GeV polarized $p$$+$$p$ collisions. Comparison of the ${\pi }^0$ results with different theory expectations based on fits of other published data showed a preference for small positive values of gluon polarization, $\Delta G$, in the proton in the probed Bjorken $x$ range. The effect of adding the new 2009 \pz data to a recent global analysis of polarized scattering data is also shown, resulting in a best fit value $ΔG^{[0.05,0.2]}_{\mbox{DSSV}} = 0.06^{+0.11}_{-0.15}$ in the range $0.05<x<0.2$, with the uncertainty at $\Delta {\chi }^2=9$ when considering only statistical experimental uncertainties. Shifting the PHENIX data points by their systematic uncertainty leads to a variation of the best-fit value of $ΔG^{[0.05,0.2]}_{\mbox{DSSV}}$ between $0.02$ and $0.12$, demonstrating the need for full treatment of the experimental systematic uncertainties in future global analyses.

380 authors, 19 pages, 14 figures, 7 tables. Submitted to Phys. Rev. D. 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

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• Global Analysis of Helicity Parton Densities and Their Uncertainties
• Global Analysis of Fragmentation Functions for Protons and Charged Hadrons
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• QCD Analysis of the Polarized World Data
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• High transverse momentum eta meson production in p+p, d+Au and Au+Au collisions at sqrt(s_NN) = 200 GeV
• Determination of gluon polarization from deep inelastic scattering and collider data
• Global Analysis of Fragmentation Functions for Eta Mesons
• Proper identification of the gluon spin

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