Accessing gluon GTMD $F^g_{1,4}$ via the $\langle\sin(2\phi)\rangle$ azimuthal asymmetry of exclusive $\pi^0$ production in $ep$ collisions

TL;DR

This paper proposes a method to access the gluon GTMD $F_{1,4}^g$ through the $ ext{sin}(2 ext{phi})$ azimuthal asymmetry in exclusive $ ext{pi}^0$ production in electron-proton collisions, offering predictions for future collider experiments.

Contribution

It presents the first model calculation of the imaginary part of $F_{1,4}^g$ and predicts measurable asymmetries at upcoming Electron-Ion Colliders.

Findings

Computed gluon distributions using a light-front spectator model.

Predicted $ ext{sin}(2 ext{phi})$ asymmetries relevant for EIC and EicC.

Highlighted the role of Coulomb-nuclear interference and Primakoff process.

Abstract

The longitudinal single-target spin asymmetry in exclusive $\pi^0$ production in $ep$ collisions is a sensitive probe of the imaginary part of the gluon generalized transverse momentum dependent distribution $F_{1,4}^g$. It appears as a characteristic $\sin(2\phi)$ azimuthal correlation between the transverse momenta of the scattered electron and the recoil proton, generated by Coulomb-nuclear interference; consequently, the Primakoff process should be included. We compute the relevant gluon distributions in a light-front spectator model of the proton that explicitly incorporates gluonic degrees of freedom. This work presents the first model calculation of the imaginary part of $F_{1,4}^g$ and delivers predictions for the resulting asymmetries in kinematics relevant to the planned Electron-Ion Colliders (EIC and EicC), providing theoretical predictions for upcoming measurements.