Inclusive $A_{LL}$ Measurements at STAR

TL;DR

This paper reports on STAR's measurements of the double-spin asymmetry $A_{LL}$ in proton-proton collisions at RHIC, providing new insights into the gluon polarization within the proton and informing global analyses.

Contribution

It presents new experimental measurements of $A_{LL}$ for jets and pions at 200 GeV, offering valuable constraints on gluon polarization in the proton.

Findings

Measurements constrain gluon polarization in the proton.

Results are incorporated into global analyses.

Future measurement plans are discussed.

Abstract

One of the primary goals of the RHIC Spin program is to determine the gluon polarization distribution within the proton. At leading order, $pp$ collisions involve a mixture of quark-quark, quark-gluon, and gluon-gluon scattering. In RHIC, the gluon-gluon and quark-gluon contributions dominate, making the accelerator an ideal tool to explore gluon polarization. The STAR experiment has measured the longitudinal double-spin asymmetry $A_{LL}$ for inclusive production of jets and pions, and for charged pion production opposite a jet, at $\sqrt{s} = 200 GeV$. The results provide valuable new constraints on the gluon polarization in the proton when included in a next-to-leading-order global analysis. The current status of the STAR measurements and the plans for future measurements will be discussed.