Measurement of Transverse Single Spin Asymmetry AN in Eta Mass Region at Large Feynman XF with the STAR Forward Pion Detector
Abstract
The large values of the transverse single spin asymmetry, AN, seen in forward pi0 production from polarized proton collisions have stimulated important questions and have been studied in QCD based transverse spin models. We report the first RHIC measurement of AN for the two photon mass region of the eta meson. The eta peak for meson energies greater than 50 GeV (Feynman xF >0.5) was observed in the STAR Forward Pion Detectors, along with pi0 mesons, at pseudo-rapidity of 3.65 in sqrts=200 GeV pp collisions. The pi0 transverse asymmetry, which has already been reported in detail by the STAR collaboration, is compared to the transverse asymmetry in the eta mass region. The surprising observation is that in this kinematic region, the eta asymmetry is larger than the already large pi0 asymmetry.