Extraction of electromagnetic properties of the Δ(1232) excitation from pion photoproduction

Several methods for the treatment of pion photoproduction in the region of the Δ(1232) resonance are discussed, in particular the effective Lagrangian approach and the speed plot analysis are compared to a dynamical treatment. As a main topic, we discuss the extraction of the genuine resonance parts of the magnetic dipole and electric quadrupole multipoles of the electromagnetic excitation of the resonance. To this end, we try to relate the various values for the ratio $R_{\mathrm{EM}}$ of the $E2\mathrm{}$ to $M1\mathrm{}$ multipole excitation strengths for the Δ(1232) resonance as extracted by the different methods to corresponding ratios of a dynamical model. Moreover, it is confirmed that all methods for extracting resonance properties suffer from an unitary ambiguity which is due to some phenomenological contributions entering the models.