"Figure 2b" of "Measurement of Transverse Single-Spin Asymmetries for J/psi Production in Polarized p+p Collisions at sqrt(s) = 200 GeV"

We report the first measurement of transverse single-spin asymmetries in $J/\psi$ production from transversely polarized $p$+$p$ collisions at $\sqrt{s}$ = 200 GeV with data taken by the PHENIX experiment in 2006 and 2008. The measurement was performed over the rapidity ranges 1.2 < $|y|$ < 2.2 and $|y|$ < 0.35 for transverse momenta up to 6 GeV/$c$. $J/\psi$ production at RHIC is dominated by processes involving initial-state gluons, and transverse single-spin asymmetries of the $J/\psi$ can provide access to gluon dynamics within the nucleon. Such asymmetries may also shed light on the long-standing question in QCD of the $J/\psi$ production mechanism. Asymmetries were obtained as a function of $J/\psi$ transverse momentum and Feynman-$x$. In this paper, we calculated $$ separately for the north and south muon spectrometers. The new combined spin asymmetry in the forward region is $A_N$ = -0.026 $\pm$ 0.026$^{stat}$ $\pm$ 0.003$^{syst}$. Since this asymmetry is consistent with zero, we no longer claim that our results suggest a possible nonzero trigluon correlation function in transversely polarized protons.

Transverse single-spin asymmetry of $J/\psi$ mesons plotted against $J/\psi$ transverse momentum. Systematic uncertainties $\delta$$A^f_N$ Type B and $\delta$$A^P_N$ Type B are due to the geometric scale factor and the polarization, respectively.