PION AND PHOTON COUPLINGS OF N-ASTERISK RESONANCES FROM SCATTERING ONTHE PROTON

Results of a relativistic model for pion- and photon-induced reactions on the proton are presented. The model is crossing symmetric and gaug e invariant. The nucleon resonances P-11(1440), P-11(1710), D-13(1520) , S-11(1535), S-11(1650), P-33(1232), P-33(1600), S-31(1620), and D-33 (1700) have been included explicitly in the calculation. Unitarity wit hin the channel space pi N circle plus gamma N below the two-pion prod uction threshold has been achieved by using the K-matrix approach. Str ong and electromagnetic coupling parameters of the N resonances have been determined from a fit to the pion-nucleon phase shifts, pion-phot oproduction multipoles and Compton-scattering cross sections. The mode l is shown to describe simultaneously most of the available data. Resu lts for the electric and magnetic polarizabilities of the nucleon are presented. (C) 1998 Elsevier Science B.V. All rights reserved.