Model-independent determination of K-matrix poles and residues in the Delta (1232) region from the multipole data for pion photoproduction.

Abstract

Using only the analytic structure of the $K$ matrix and the assumption that the Compton-scattering amplitude is small compared to strong and electrostrong amplitudes, we extract the pole position and the residues for the resonant multipoles, in a model-independent and background-free fashion, directly from the experimentally obtained multipole data base in the $\ensuremath{\Delta}(1232)$ region, posing a challenge for QCD-inspired hadron models.