# Suppression of maximal linear gluon polarization in angular asymmetries

## TL;DR

This paper analyzes how TMD evolution suppresses the azimuthal asymmetry caused by linearly polarized gluons in unpolarized proton-nucleus collisions, highlighting the potential for experimental detection at RHIC and LHC.

## Contribution

It demonstrates the impact of TMD evolution on gluon polarization asymmetries and identifies optimal conditions for experimental measurement at collider facilities.

## Key findings

- TMD evolution causes significant suppression of the asymmetry at higher invariant masses.
- The asymmetry remains detectable at moderate virtualities at RHIC and LHC.
- The process provides a clean test for the $k_t$-resummation formalism in small-$x$ physics.

## Abstract

We perform a phenomenological analysis of the $\cos 2 \phi $ azimuthal asymmetry in virtual photon plus jet production induced by the linear polarization of gluons in unpolarized $pA$ collisions. Although the linearly polarized gluon distribution becomes maximal at small $x$, TMD evolutionleads to a Sudakov suppression of the asymmetry with increasing invariant mass of the $\gamma^*$-jet pair. Employing a small-$x$ model input distribution, the asymmetry is found to be strongly suppressed under TMD evolution, but still remains sufficiently large to be measurable in the typical kinematical region accessible at RHIC or LHC at moderate photon virtuality, whereas it is expected to be negligible in $Z/W$-jet pair production at LHC. We point out the optimal kinematics for RHIC and LHC studies, in order to expedite the first experimental studies of the linearly polarized gluon distribution through this process. We further argue that this is a particularly clean process to test the $k_t$-resummation formalism in the small-$x$ regime.