Sensitivity of Double Deeply Virtual Compton Scattering observables to GPDs

TL;DR

This paper investigates how Double Deeply Virtual Compton Scattering (DDVCS) observables are sensitive to proton GPDs, providing insights for future measurements at CEBAF and EIC using polarized beams and targets.

Contribution

It offers a comprehensive analysis of DDVCS observables' sensitivity to GPDs, highlighting potential for improved GPD extraction at upcoming facilities.

Findings

DDVCS observables show significant sensitivity to proton GPDs.

Polarized electron and positron beams enhance GPD measurement capabilities.

Results inform experimental strategies at CEBAF and EIC.

Abstract

Generalized Parton Distributions (GPDs) are multidimensonal structure functions that encode the information about the internal structure of hadrons. Using privileged channels such as Deeply Virtual Compton Scattering (DVCS) or Timelike Compton Scattering (TCS), it is possible to make direct measurements at points where the momentum fraction of the parton equals the respective scaling variable. Double Deeply Virtual Compton Scattering (DDVCS) is a not yet measured and promising channel for GPD studies as it allows to perform more general measurements at independent momentum fraction and scaling variable values. GPDs are extracted from Compton Form Factors which arise naturally in experimental observables from different combinations of beam and target configurations. In the context of the Continuous Electron Beam Accelerator Facility (CEBAF) and the Electron Ion Collider (EIC), we report the results of an exhaustive study of the DDVCS observables from polarized electron and positron beams directed to a polarized proton target. The study focuses on the sensitivity of the observables to the parton helicity conserving proton GPDs, particularly the consequences for GPDs measurements via DDVCS at CEBAF and EIC based on the VGG and GK19 model predictions.