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

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.