Speakers
Description
We report a new measurement of transverse single-spin asymmetries for pair-production of jets in collisions of transversely polarized protons at $\sqrt{s}$ = 200 GeV with data taken in 2012 and 2015 at STAR. In this measurement we probe, at high $Q^2$, correlations between the transverse spin ($\vec S$) of a proton, moving in the longitudinal ($\vec p$) direction, and the transverse momenta of partons ($\vec k_T$) within the proton. A non-zero correlation -- the Sivers effect -- results in a spin-dependent shift in the dijet azimuthal opening angle away from 180$^\circ$. The corresponding $\langle k_T \rangle$ is then calculated based on a simple kinematic model. By using charge-tagging of the jets to enhance either $u$- or $d$-quark contributions, we see a non-zero Sivers effect for the first time in dijet production in high-energy proton collisions. The individual parton contributions ($u$, $d$, gluon+sea) to the measured $\langle k_T \rangle$ are extracted through a matrix inversion of the charge-sorted $\langle k_T \rangle$ data. Preliminary results and status of the analysis will be presented.
