Unified Chew-Mandelstam SAID analysis of pion photoproduction data

Background: The determination of the scattering and reaction amplitudes of hadronic and electromagnetic probes on the single nucleon is of central importance in determining the resonance properties of the nucleon and, in turn, the confining properties of QCD. Purpose: To achieve in a Chew-Mandelstam parametrization a unified description of single-pion photoproduction data, together with that of pion- and eta-hadroproduction data, which is consistent with unitarity at the two-body level. Methods: Energy-dependent and single-energy partial-wave analyses of pion photoproduction data have been performed and compared to previous SAID fits and multipoles and to those from the Mainz and Bonn-Gatchina groups. Results: The new, unified fit is more economical, using fewer parameters, as a result of the consistent implementation of two-body unitarity. Some low-energy structures, not seen by other groups, are no longer present in the current CM12 fit. Additionally, its multipole phases, particularly that of E-0+(1/2), have changed. Photo-decay couplings extracted from CM12 are generally-although not completely-in agreement with an earlier SAID fit (SN11) and the PDG values; significant differences are seen in N(1535)S-11 and N(1720)P-13.