Transverse spin physics at STAR

The transverse spin physics program at STAR is pursuing two complementary goals. The first is to extract quark transversity, and the second is to understand the origin of large transverse single spin asymmetry (AN) observed in the forward region. The mid-rapidity Collins and Interference Fragmentation Function (IFF) measurements at √ s = 200 GeV are aimed at the extraction of transversity. In the forward region, the measurements of inclusive π0 and η meson AN, as functions of xF and pT at √ s = 200 GeV and 500 GeV, allow for comparisons against theoretical models that incorporate the effects of either higher-twist, or partonic transverse momenta. The planned forward upgrade will enable the measurements of AN for prompt photons, jets, and the Drell-Yan process.