Extracting Nucleon Resonance Transition GPDs from $e^- N\to e^-\gamma N\pi$ Deeply Virtual Compton Scattering

TL;DR

This paper explores how Deeply Virtual Compton Scattering (DVCS) can be used to extract nucleon resonance transition GPDs, highlighting the significance of background processes and interference effects in experimental measurements.

Contribution

It introduces a detailed analysis of background pion emission processes in DVCS and their impact on resonance excitation measurements, aiding the extraction of nucleon transition GPDs.

Findings

Interference effects can significantly alter cross sections.

Background processes contribute notably in certain kinematic regions.

DVCS can effectively probe nucleon resonance structures.

Abstract

We investigate the process in which Deeply Virtual Compton Scattering (DVCS) excites a baryon resonance. In particular, we assess, in DVCS leading to the Roper resonance, the relative importance of a "background'' process in which a pion is first emitted by the nucleon, which then undergoes a DVCS event. Our numerical results, using realistic DVCS kinematics, indicate that there can be measurable interference effects. They suggest that this process could substantially modify the experimentally observed cross sections at CLAS12-like kinematics, motivating their inclusion in precision analyses of DVCS experiments. We further find that in spite of this background, the transition to a Roper-like state through DVCS does contribute significantly to the $e^- N\to e^-\gamma N\pi$ cross section in some kinematic regions. This suggests that the creation of nucleon resonances via DVCS is a useful method for extracting information about the nucleon transition GPDs and the internal structure of the excited states.