Introduction

A chief aim of the Electron-Ion Collider (EIC) is to probe the origin of the proton’s spin.

Decades ago, experiments revealed that the proton’s total spin cannot be accounted for

by a simple three-quark model. This “spin crisis” suggests that gluon dynamics play a

critical role in proton spin. This is especially important at small-x (large energies) where

gluons dominate the proton’s structure. Exclusive vector meson (VM) production from

polarized electron-proton collisions provides a clean probe of gluons in the small-x

regime. In an effort to uncover the spatial distributions of these gluons and how they

contribute to proton spin, we analyzed spin-dependent effects in these reactions by

predicting theoretical spin asymmetries to be measured by the future EIC.

Generalized Parton Distributions (GPDs) describe correlations between quark/gluon

momentum and spatial positions, offering a 3D image of protons. Measuring GPDs is

essential to understanding the proton’s spin structure. However, they are virtually

unknown and difficult to model. This project focuses the double spin asymmetry in

exclusive VM production, a novel observable, as a sensitive probe of GPDs and related

spin-dependent dynamics.

Methods

Goal: Calculate the expected double spin asymmetry (DSA) in

exclusive VM production and assess its potential to reveal GPDs.

Approach:

➢ Parameterize amplitudes with polarization dependencies

➢ Expand to leading-twist (small momentum transfer) to isolate

dominant spin effects

➢ Compute double spin asymmetry for transversely polarized proton and longitudinally

polarized electron

➢ Connect results to GPDs

➢ Validate results with previous predictions

➢ Predict numerical estimates for the EIC

Results & Conclusions