Accessing the gluon GTMD $\boldsymbol{F_{1,4}}$ in exclusive $\boldsymbol{\pi^0}$ production in $\boldsymbol{ep}$ collisions

TL;DR

This paper shows how the longitudinal single target-spin asymmetry in exclusive $$ production in $ep$ collisions can reveal the imaginary part of the gluon GTMD $F_{1,4}$, providing a new way to probe gluon distributions.

Contribution

It introduces a method to access the gluon GTMD $F_{1,4}$ via spin asymmetries in exclusive $$ production, with numerical estimates for EIC and EicC.

Findings

Identifies the $$ spin asymmetry as a probe for gluon GTMDs.

Predicts a $\u03c6$-dependent azimuthal asymmetry in the process.

Provides numerical estimates for experimental conditions.

Abstract

We demonstrate that the longitudinal single target-spin asymmetry in exclusive $\pi^0$ production in $ep$ collisions can give access to the imaginary part of the gluon generalized transverse momentum distribution (GTMD) $F_{1,4}$. Such a longitudinal spin asymmetry that results from the Coulomb-nuclear interference effect, leads to a characteristic azimuthal angular correlation of $\sin 2\phi$, where $\phi$ is the azimuthal angle between the scattered lepton transverse momentum and the recoiled proton's transverse momentum. We also present a numerical estimate of the asymmetry for the kinematics accessible at EIC and EicC.