Single Spin Asymmetry Scaling in the Forward Rapidity Region at RHIC

TL;DR

This paper studies how single spin asymmetries in forward hadron production at RHIC exhibit geometric scaling with transverse momentum, using a new fragmentation function approach, and proposes a method to probe nuclear saturation effects.

Contribution

It introduces a transverse momentum dependent Collins fragmentation function to analyze the scaling of spin asymmetries in high-energy collisions.

Findings

Experimental data shows transverse-momentum-dependent geometric scaling.

The scaling analysis aligns with observed spin asymmetry patterns.

Proposes a method to probe nuclear saturation scale via normalized spin asymmetries.

Abstract

We investigate the scaling properties in inclusive hadron production and the associated single transverse spin asymmetry in the forward rapidity region at RHIC. We find that the spin-averaged experimental data in both $pp$ and $dAu$ collisions demonstrates a transverse-momentum-dependent geometric scaling. We introduce the transverse momentum dependent Collins fragmentation function to study the scaling of the single transverse spin asymmetries. The general feature of the scaling analysis is consistent with the experimental observations, in particular, for the transverse momentum dependence of the spin asymmetries at RHIC energy. We further propose to probe the saturation scale of nucleus by measuring the spin asymmetry normalized by that in $pp$ scattering at low transverse momentum.