Speaker
Prof.
Carl Gagliardi
(Texas A&M University)
Description
The STAR Collaboration at RHIC is exploring the partonic origin of the proton spin with a broad range of measurements in polarized pp collisions. STAR measurements of the transverse single-spin asymmetry, $A_N$, for $W$ boson production provide the first experimental investigation of the non-universality of the Sivers function. Precise follow-up measurements of $A_N$ for direct photon production, Drell-Yan di-electron production, and $W$ boson production are underway that will both provide a definitive test of the non-universality and constrain evolution of transverse-momentum-dependent distributions (TMDs) over a very wide $Q^2$ range. STAR has measured di-pion interference fragmentation functions and the transverse single-spin dependence of the azimuthal modulation of pions in jets in pp collisions at $\sqrt{s}$ = 200 and 500 GeV. The results provide the first observations of transversity in pp collisions, and enable tests of universality and factorization-breaking effects for TMDs in hadronic interactions. Additional transverse modulations provide limits on gluon linear polarization in polarized protons and the twist-3 analog of the gluon Sivers distribution. The current status of these analyses and the prospects to extend them in the near future will be discussed.
Primary author
Prof.
Carl Gagliardi
(Texas A&M University)
