Measurement of longitudinal spin asymmetries for weak boson production in polarized proton-proton collisions at RHIC

TL;DR

This paper reports measurements of spin asymmetries in weak boson production in polarized proton collisions at RHIC, providing insights into the proton's polarized quark distributions and favoring a positive up antiquark polarization.

Contribution

It presents the first measurements of single- and double-spin asymmetries for W and Z bosons at RHIC, offering new constraints on polarized quark distributions in the proton.

Findings

Results favor a sizable, positive up antiquark polarization.

Asymmetries measured as a function of decay lepton pseudorapidity.

Comparison with theoretical predictions supports existing models.

Abstract

We report measurements of single- and double- spin asymmetries for $W^{\pm}$ and $Z/\gamma^*$ boson production in longitudinally polarized $p+p$ collisions at $\sqrt{s} = 510$ GeV by the STAR experiment at RHIC. The asymmetries for $W^{\pm}$ were measured as a function of the decay lepton pseudorapidity, which provides a theoretically clean probe of the proton's polarized quark distributions at the scale of the $W$ mass. The results are compared to theoretical predictions, constrained by recent polarized deep inelastic scattering measurements, and show a preference for a sizable, positive up antiquark polarization in the range $0.05<x<0.2$.