Probing Orbital Angular Momentum Distributions in Elastic Vector Meson Production in Longitudinally Polarized Electron--Proton Scattering

Abstract

We consider elastic vector meson production in longitudinally polarized electron-proton collisions at small $x$. Inspired by previous pioneering proposals in the literature, we calculate the numerator of the longitudinal double-spin asymmetry (DSA) within the polarized small-$x$ formalism for both the transversely and longitudinally polarized vector mesons. Our calculation demonstrates that the $\cos {\varphi }_{k\Delta }$ azimuthal harmonic of the DSA for the elastic vector meson production at small transverse momentum transfer (with ${\varphi }_{k\Delta }$ the azimuthal angle between the transverse momenta of the outgoing electron and meson in the dipole/Trento frame) provides a promising probe of the orbital angular momentum (OAM) distributions at small $x$. Our results can be applied to several different vector meson species, thus opening up a new class of observables that can be used to extract OAM distributions from experimental data.

arXiv comment29 pages, 3 figures