High precision cross section and polarization data in meson photoproduction have become a broad source of information about excited nucleons. The main focus of this collaboration is a unique extraction of partial wave amplitudes and resonance parameters from the available data without assuming any explicit reaction model. This will be achieved by taking into account the fixed-t analytic properties of the underlying amplitudes. The method originates from the Karlsruhe-Helsinki PWA of πN scattering where an efficient method for imposing constraints from fixed-t analyticity was developed and applied. Our goal is to adapt this strategy to photoproduction and to implement it in single-energy partial wave analyses.
Furthermore, the pole positions and residues from meson photoproduction multipoles will be determined by exploiting the knowledge about the analytic structure of each partial wave. Instead of using a model, an expansion based on a Laurent series of the partial wave T-matrices, with a Pietarinen series representing the regular part of the amplitudes (”L+P expansion”) will be used.