Linearly polarized gluon effects in unpolarized collisions

TL;DR

This paper explores how linearly polarized gluons inside unpolarized hadrons influence particle production at the LHC and EIC, providing predictions and potential experimental tests for their effects.

Contribution

It introduces a framework for predicting linear gluon polarization effects in unpolarized collisions and discusses their potential observability at current and future colliders.

Findings

Linear gluon polarization affects Higgs and quarkonium production at a few percent level.

Predictions vary significantly for quarkonium production, indicating larger effects.

Experimental measurements at EIC could determine the size and sign of gluon polarization.

Abstract

Linear polarization of gluons inside unpolarized hadrons affects the transverse momentum distribution of produced spin-0 particles, such as of the Higgs or (pseudo-)scalar quarkonium states at LHC. Despite the currently unknown amount of linear gluon polarization, a range of predictions can be obtained, using TMD evolution, which indicates that their effect is on the few percent level in Higgs production, but can be much larger in quarkonium production. Together with asymmetries in open charm or bottom production in electro-production at an Electron-Ion Collider, the size and sign of the linear gluon polarization could be extracted experimentally. These processes also allow to test the behavior expected at small $x$ in and outside the saturation region.