Inclusive Jet Measurements in Longitudinally Polarized proton-proton Collisions at STAR

TL;DR

This paper reports on measurements of inclusive jet production and double spin asymmetries in polarized proton-proton collisions at STAR, providing insights into gluon polarization and testing perturbative QCD predictions at different energies.

Contribution

It presents new measurements of jet cross-sections and spin asymmetries at 200 and 510 GeV, advancing understanding of gluon polarization in the proton.

Findings

Jet cross-sections agree with NLO pQCD calculations after corrections.

Evidence of non-zero gluon polarization for x > 0.05.

Exploration of gluon polarization down to x ~ 0.02.

Abstract

Jet production in high energy proton-proton ($p+p$) collisions is dominated by hard QCD subprocesses such as gluon-gluon and quark-gluon scatterings. Therefore $p+p$ is an effective tool to probe the internal distribution of gluons in the proton. The STAR Collaboration at the Relativistic Heavy Ion Collider (RHIC) is using longitudinally polarized $p+p$ collisions at the center of mass energies, $\sqrt{s} = $ 200 and 510 GeV, to study the cross-section and double spin asymmetries, $A_{LL}$, of inclusive jet and di-jet production. The measurements at $\sqrt{s} = $ 200 GeV showed that the jet cross-sections are well described by the next-to-leading-order perturbative QCD calculations after underlying event and hadronization corrections. The previous 2009 $\sqrt{s} = $ 200 GeV inclusive jet asymmetry $A_{LL}$ measurement at pseudo-rapidity $|\eta| < $ 1.0 showed the first experimental evidence of a non-zero gluon polarization for partonic momentum fraction, $x > 0.05$. The inclusive jet $A_{LL}$ measurement at $\sqrt{s} = $ 510 GeV allows to explore the gluon polarization to smaller $x \sim 0.02$. The 2012 inclusive jet $A_{LL}$ and cross-section measurements at $\sqrt{s} =$ 510 GeV, the techniques used in the jet analysis including underlying event correction, and future perspectives related to jet measurements at STAR will be presented.