# Longitudinal Double-Spin Asymmetries for Forward Di-jet Production in Polarized $pp$ Collisions at $\sqrt{s}$ = 200 GeV

## TL;DR

This paper reports measurements of double-spin asymmetries in forward di-jet production in polarized proton-proton collisions at 200 GeV, providing insights into the gluon spin contribution to the proton, especially at low momentum fractions.

## Contribution

It presents the first forward di-jet asymmetry measurements at RHIC, offering tighter constraints on the gluon polarization distribution $\Delta g(x)$ at low $x$ compared to previous inclusive jet results.

## Key findings

- Evidence for non-zero gluon polarization at $x > 0.05$
- Preliminary asymmetry results at forward rapidity
- Enhanced constraints on $\Delta g(x)$ at low $x$

## Abstract

One of the primary goals of the STAR spin program is to determine the contribution of the gluon spin ($\Delta G$) to that of the proton. Recent measurements of the longitudinal double-helicity asymmetry, $A_{LL}$, from inclusive jets place strong constraints on the spin-dependent gluon distribution $\Delta g(x)$ and, for the first time, find evidence for non-zero gluon polarization values for partonic momentum fraction $x$ greater than 0.05. In contrast to inclusive jets, di-jet correlation measurements provide access to partonic kinematics, at leading order, and thus give tighter constraints on the behavior of $\Delta g$ as a function of gluon momentum fraction. Furthermore, di-jet measurements at forward rapidity probe the lower $x$ values where $\Delta g(x)$ is poorly constrained. Preliminary $A_{LL}$ results for di-jets with $-0.8 < \eta_1 < 0.8$ and $0.8 < \eta_2 < 1.8$, from polarized $pp$ collisions at $\sqrt{s}$ = 200 GeV, are presented.