Inclusive double-helicity asymmetries in neutral-pion and eta-meson production in p → + p → collisions at s =200GeV

Abstract

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 π 0 and η production in ffiffiffi s p ¼ 200 GeV polarized p þ p collisions. Comparison of the π 0 results with different theory expectations based on fits of other published data showed a preference for small positive values of gluon polarization, Δ G , in the proton in the probed Bjorken x range. The effect of adding the new 2009 π 0 data to a recent global analysis of polarized scattering data is also shown, resulting in a best fit value Δ G ½ 0 . 05 ; 0 . 2 DSSV ¼ 0 . 06 þ 0 . 11 − 0 . 15 in the range 0 . 05 <x< 0 . 2 , with the uncertainty at Δ χ 2 ¼ 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 Δ G ½ 0 . 05 ; 0 . 2 DSSV between 0.02 and 0.12, demonstrating the need for full treatment of the experimental systematic uncertainties in future global analyses.