Measurement of the transverse single-spin asymmetry in $p^\uparrow+p \to W^{\pm}/Z^0$ at RHIC

TL;DR

This paper reports the first measurement of the transverse single-spin asymmetry in weak boson production in polarized proton collisions, testing the non-universality of the Sivers function predicted by QCD.

Contribution

It provides the first experimental investigation of the non-universality of the Sivers function in proton-proton collisions at RHIC.

Findings

Measured asymmetry sensitive to the Sivers function

First test of Sivers function sign change in proton-proton collisions

Supports non-universality prediction of QCD

Abstract

We present the measurement of the transverse single-spin asymmetry of weak boson production in transversely polarized proton-proton collisions at $\sqrt{s} = 500~\text{GeV}$ by the STAR experiment at RHIC. The measured observable is sensitive to the Sivers function, one of the transverse momentum dependent parton distribution functions, which is predicted to have the opposite sign in proton-proton collisions from that observed in deep inelastic lepton-proton scattering. These data provide the first experimental investigation of the non-universality of the Sivers function, fundamental to our understanding of QCD.