Recent results of gluon and sea quark polarization measurements in polarized proton-proton collisions at STAR

TL;DR

The STAR experiment's recent measurements in polarized proton-proton collisions reveal a non-zero gluon contribution to proton spin and provide insights into sea quark polarization, advancing understanding of proton internal structure.

Contribution

This paper presents the first evidence of a non-zero gluon polarization contribution and new measurements of sea quark polarization in proton spin structure at RHIC.

Findings

First non-zero gluon contribution to proton spin for 0.05<x<1

Direct probe of polarized anti-u and anti-d quark distributions

Enhanced constraints on proton spin components

Abstract

The STAR experiment at RHIC is carrying out a comprehensive high-energy spin physics program to understand the internal structure and dynamics of the proton in polarized proton-proton collisions at $\sqrt{s} = 200$ GeV and $\sqrt{s} = 500/510$ GeV. STAR has the capability, with nearly full azimuthal coverage, to reconstruct leptons, hadrons and jets in the mid-rapidity region ($|\eta|<1$). The results for inclusive jet longitudinal double spin asymmetries taken during the 2009 RHIC run indicate the first non-zero gluon contribution ($\Delta g(x,Q^{2}) / g(x,Q^{2})$) to the proton spin for $0.05<x<1$ (Bjorken-x: momentum fraction of partons). Recent longitudinal single-spin asymmetry measurements of $W^{+/-}$ bosons at $\sqrt{s} = 500/510$ GeV in polarized proton-proton collisions provide a direct probe of the polarized anti-u and anti-d quark distributions ($\Delta \bar{u}(x,Q^{2})$, $\Delta \bar{d}(x,Q^{2})$). These results better constrain the polarized gluon and sea quark distributions of the proton in the RHIC sensitive kinematic region. Future measurements with continuing high energy polarized proton-proton run at RHIC and detector upgrade will explore the gluonic contribution to the proton spin in extended range.