Gluon orbital angular momentum at small-$x$

TL;DR

This paper analyzes the gluon orbital angular momentum distribution at small-x, deriving a new operator representation, and links it to gluon helicity, providing a way to probe gluon spin structure via diffractive dijet production.

Contribution

It introduces a novel operator representation of gluon OAM at small-x and relates it to gluon helicity, offering new insights into gluon spin structure.

Findings

Derived a new operator form of gluon OAM in terms of Wilson lines.

Showed that gluon OAM is approximately proportional to gluon helicity at small-x.

Proposed diffractive dijet asymmetry as a probe of gluon spin and OAM.

Abstract

We present a general analysis of the orbital angular momentum (OAM) distribution of gluons $L_g(x)$ inside the nucleon with particular emphasis on the small-$x$ region. We derive a novel operator representation of $L_g(x)$ in terms of Wilson lines and argue that it is approximately proportional to the gluon helicity distribution $L_g(x) \approx -2\Delta G(x)$ at small-$x$. We also compute longitudinal single spin asymmetry in exclusive diffractive dijet production in lepton-nucleon scattering in the next-to-eikonal approximation and show that the asymmetry is a direct probe of the gluon helicity/OAM distribution as well as the QCD odderon exchange.