Speaker
Description
Generalised parton distributions (GPDs) provide a three-dimensional description of hadron structure and offer a framework for investigating the internal structure of nucleon resonances. We study deeply virtual Compton scattering with an associated pion in the final state, $eN\rightarrow e\gamma N\pi$, where the $N\pi$ system provides access to both conventional nucleon GPDs and nucleon-to-resonance transition GPDs.
A phenomenological description of this process is developed including deeply virtual Compton scattering, Bethe–Heitler production, and their interference. Both diagonal mechanisms and direct transitions to the $P_{11}(1440)$ Roper and $S_{11}(1535)$ resonances are considered. The diagonal amplitude is projected onto the corresponding $N\pi$ partial waves, allowing a consistent comparison with the resonant contributions. Final-state interactions are incorporated through phase-shift and coupled-channel $K$-matrix treatments.
Numerical results at JLab-like kinematics demonstrate the relative importance of the two mechanisms and show that final-state interactions can substantially modify the extracted resonance-region observables. Implications for accessing transition GPDs in future measurements are discussed.