Single Spin Asymmetry in Forward $pA$ Collisions

TL;DR

This paper calculates the transverse single spin asymmetry in forward proton-proton and proton-nucleus collisions, highlighting the impact of gluon saturation effects and the cancellation of nuclear effects in asymmetry measurements.

Contribution

It introduces the inclusion of gluon saturation effects in the calculation of single spin asymmetries, revealing the cancellation of nuclear effects in the asymmetry.

Findings

Nuclear effects cancel in the asymmetry at large $x_F$.

Soft fermionic pole disappears in saturation environment.

Predictions testable at RHIC.

Abstract

We compute the transverse single spin asymmetry in light hadron production $p^\uparrow p\to hX$ and $p^\uparrow A\to hX$ including the gluon saturation effect in the unpolarized nucleon/nucleus. In the forward (large-$x_F$) region, the dominant contribution comes from the so-called derivative term associated with the soft gluonic pole. This leads to the cancellation of nuclear effects in $A_N$ which can be tested at RHIC. We also show that the soft fermionic pole disappears in the saturation environment.