Twist corrections to exclusive vector meson production in a saturation framework

TL;DR

This paper introduces a comprehensive framework combining higher-twist formalism with small-x physics to analyze exclusive vector meson production, addressing end-point singularities and enabling studies of the dilute-to-dense QCD transition.

Contribution

It develops a novel approach integrating higher-twist effects with semi-classical small-x physics, applicable to a broad kinematic range including non-forward scattering.

Findings

Derived a general formula for transversely polarized vector meson production.

Implemented Wilson line expansion in Reggeized gluon fields within the BFKL approximation.

Facilitated investigation of the dilute-to-dense QCD regime transition.

Abstract

We develop a framework combining the higher-twist formalism of exclusive processes in the $s$ channel with the semi-classical effective description of small-$x$ physics in the $t$ channel. We apply it to transversely polarized light vector meson production, $\gamma^{*} p \rightarrow V (\rho, \varphi ,\omega) \; p$, which starts at the next-to-leading power and for which a purely collinear treatment leads to end-point singularities. The result is obtained in the most general kinematics, including both forward and non-forward cases by preserving the full impact parameter dependence in the non-perturbative correlators, in both momentum and coordinate space representations. A systematic expansion of the Wilson lines in terms of Reggeized gluon fields is performed in order to obtain the results in the weak-field BFKL approximation. These new results will allow for investigating the dilute-to-dense regime transition of QCD for a wide class of observables.