Transverse single-spin asymmetries of midrapidity $\pi^0$ and $\eta$ mesons in polarized $p$$+$$p$ collisions at $\sqrt{s}=200$ GeV

TL;DR

This paper reports precise measurements of transverse single-spin asymmetries for neutral pions and eta mesons in polarized proton-proton collisions at 200 GeV, providing insights into nonperturbative QCD effects and parton flavor contributions.

Contribution

It presents the most precise asymmetry measurements for these mesons at this energy, enabling better constraints on twist-3 and gluon Sivers functions.

Findings

Asymmetries are measured with three times smaller uncertainties than previous results.

Results can help disentangle effects of strangeness, isospin, and mass on asymmetries.

Data constrains theoretical models of nonperturbative QCD effects.

Abstract

We present a measurement of the transverse single-spin asymmetry for $\pi^0$ and $\eta$ mesons in $p^\uparrow$$+$$p$ collisions in the pseudorapidity range $|\eta|<0.35$ and at a center-of-mass energy of 200 GeV with the PHENIX detector at the Relativistic Heavy Ion Collider. In comparison with previous measurements in this kinematic region, these results have a factor of 3 smaller uncertainties. As hadrons, $\pi^0$ and $\eta$ mesons are sensitive to both initial- and final-state nonperturbative effects for a mix of parton flavors. Comparisons of the differences in their transverse single-spin asymmetries have the potential to disentangle the possible effects of strangeness, isospin, or mass. These results can constrain the twist-3 trigluon collinear correlation function as well as the gluon Sivers function.