Accessing the gluon GTMD ${\mathbf{F}}_{1,4}$ in exclusive ${\mathbf{\pi }}^0$ production in $\mathbf{ep}$ collisions

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 $\sin 2\varphi$, where $\varphi$ 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.

11 pages, 2 figures