Speaker
Description
Transverse single-spin asymmetries (TSSAs) of proton-proton collisions have a history of revealing the richness of QCD. Large TSSAs were originally discovered in fixed target experiments in the mid 1970s. However they have been found to persist in collisions up to $ \sqrt{s} = 510 $ GeV and transverse momenta up to about $7$ GeV/c, well into the perturbative regime of QCD, and yet their origin remains poorly understood. The large TSSA measurements led to the development of both transverse momentum dependent descriptions and collinear twist-3 descriptions of nonperturbative spin-momentum correlations in the nucleon as well as in the process of hadronization. As hadrons, eta mesons are sensitive to both initial- and final-state nonperturbative effects for a mix of parton flavors. Their comparison to neutral pions may provide information on potential effects due to strangeness, isospin, or mass. The status of the TSSA of eta mesons at midrapidity for $200$ GeV proton-proton collisions from the PHENIX 2015 data set will be shown.
