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

TL;DR

This paper presents the first measurement of transverse single-spin asymmetries in J/psi production in polarized proton-proton collisions at 200 GeV, providing insights into gluon dynamics and J/psi production mechanisms.

Contribution

It reports the first experimental measurement of transverse single-spin asymmetries for J/psi production at RHIC energies, exploring gluon-related spin effects in polarized proton collisions.

Findings

Measured asymmetry of -0.086 in the forward region.

Indicates possible nonzero trigluon correlations.

Suggests nonzero gluon Sivers distribution function.

Abstract

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-$x$, with a value of $-0.086 \pm 0.026^{\rm stat} \pm 0.003^{\rm syst}$ in the forward region. This result suggests possible nonzero trigluon correlation functions in transversely polarized protons and, if well defined in this reaction, a nonzero gluon Sivers distribution function.