On Extraction of Twist-Two Compton Form Factors from DVCS Observables Through Harmonic Analysis

TL;DR

This paper demonstrates a model-independent method to extract all four twist-2 Compton form factors from DVCS observables using harmonic analysis, applicable at specific kinematic points and validated with simulated data.

Contribution

It introduces a harmonic analysis approach to extract all twist-2 CFFs from DVCS data without model assumptions, considering all polarization states at a fixed kinematic point.

Findings

All four twist-2 CFFs can be extracted from DVCS observables at a fixed kinematic point.

Harmonic fitting effectively retrieves CFFs from simulated cross section and asymmetry data.

Method is feasible with current experimental capabilities at JLab.

Abstract

We investigate the exercise of locally extracting the real and imaginary parts of the four twist-2 Compton form factors (CFFs) $\{\mathcal{H},\mathcal{E},\widetilde{\mathcal{H}},\widetilde{\mathcal{E}}\}$ which arise in the deeply virtual Compton scattering (DVCS) process $e + p \rightarrow e + p + \gamma$. Neglecting dynamical higher-twist contributions, we find that there are a sufficient number of DVCS observables and degrees of freedom to extract all 8 leading quantities model-independently, exploiting the azimuthal dependence of the absolute cross sections across all possible beam and target polarizations at a common kinematical point in $\{Q,t,x_B,y\}$. As an example, for typical JLab lab-frame kinematics, we simplify the reduced DVCS observables to their dominant terms, providing a sufficient number of equations for local determination of the twist-2 CFFs. We demonstrate the feasibility using harmonic fitting to both cross sections and beam spin asymmetries with both real and pseudo-data.