Fixed- t dispersion approach and single pion photoproduction in the resonance region

Abstract

The hypothesis of resonance saturation of the imaginary parts of inelastic scattering amplitudes is applied to single-pion photoproduction in the resonance region using fixed- t dispersion relations. The resonance-saturated dispersion relations are evaluated for all four charge states of the reaction, making use of knowledge of resonance photonic couplings taken from multipole analyses, and the results are compared with experimental data for cross sections and polarization asymmetries in the resonance region. Forward π + data in the fourth resonance region are fitted and couplings for the P 11 (1430) and F 37 (1940) resonance are extracted. A new value for the D 15 0(1652) coupling is proposed, and evidence is presented for non-zero values for at least two resonance couplings in the third resonance region, other than those of the spin- 5 2 resonance. The multipoles of this calculation are compared with those from phenomenological analyses of the first resonance region. The present status of the resonance-saturated fixed- t dispersion approach is discussed.