# SPIN 2018

9-14 September 2018
University of Ferrara
Europe/Rome timezone
23RD INTERNATIONAL SPIN SYMPOSIUM

## Recent Transverse Spin Measurements in pp Collisions with STAR

10 Sep 2018, 15:45
25m

### A4

Parallel Sessions 3D Structure of the Nucleon: TMDs

### Speaker

Prof. Carl Gagliardi (Texas A&amp;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&amp;M University)

 Slides