Open Access Publications from the University of California

## Measurement of Transverse Single Spin Asymmetries for $\pi^{0}$ and Jets at Large $x_{F}$ in $\sqrt{s}$ = 500 GeV Polarized Proton Collisions at STAR

• Author(s): Pan, Yuxi
The research presented in this thesis focuses on characterizing the Transverse Single Spin Asymmetries (TSSA) of inclusive $\pi^{0}$ and jet productions in polarized proton collisions at large Feynman-x ($x_{F}$) region. Theoretically these observables are explained by means of collinear twist-3 multi-parton correlations. In this picture the asymmetries originate from initial-state twist-3 parton distributions in the polarized proton and/or through the coupling between proton's initial-state transversity distribution and the final-state twist-3 fragmentation functions. The measurement of SSA for forward inclusive $\pi^{0}$ produced in $pp$ collisions up to high transverse momentum helps examine the validity and interplay of these initial- and final-state models. These models can be further explored by investigating the dependence of the TSSA on event topologies. This thesis presents the STAR measurement of TSSA for forward inclusive $\pi^{0}$ at $2.8 < \eta < 4.0$ in $\sqrt{s}$ = 500 GeV $pp$ collisions taken in 2011 with integrated luminosity of 22 $pb^{-1}$ as well as the dependence of $\pi^{0}$ TSSA on event topologies. In addition we show results of the analyses of Sivers and Collins asymmetries for forward jet-like events. The physics implications of these measurements will also be discussed.