Spin Filter in DVCS amplitudes

TL;DR

This paper reveals that angular momentum conservation issues arise in DVCS amplitudes when using reduced operators, emphasizing the importance of including longitudinal photon contributions for accurate experimental analysis.

Contribution

It demonstrates the necessity of considering longitudinally polarized virtual photons and addresses angular momentum conservation in DVCS amplitude calculations.

Findings

Angular momentum is not conserved in some DVCS kinematics with reduced operators.

Neglecting longitudinal photon contributions leads to incorrect data analysis.

Proper inclusion of all photon polarizations is essential for accurate GPD extraction.

Abstract

In deeply virtual Compton scattering (DVCS) it is found that in some kinematics angular momentum is not conserved if the amplitudes are calculated in terms of widely used reduced operators. Consequently, those kinematics will lead to the wrong analysis of experimental data in terms of generalized parton distributions. Contrary to common lore, the contribution of the longitudinally polarized virtual photon should not be neglected in the analysis of DVCS amplitudes.