Coupled K-matrix description of the reactions πN→πN, πN→ηN, γN→πN, and γN→ηN -: art. no. 035208

The coupled pi N, eta N gamma N systems are described by a K-matrix method. The parameters in this model are adjusted to get an optimal fit to pi N --> pi N, pi N --> eta N, gamma N --> pi N, and gamma N --> eta N data in an energy range of about 100 MeV each side of the eta threshold. The coupling of photons to the N(1535) state is extracted and also an alternative to the current S 11 gamma N --> pi N amplitudes suggested. Expansions are given for the eta eta and gamma eta amplitudes in terms of the eta momentum. Effects of interference of this state with background potential interactions are discussed and experimental consequences are indicated. [S0556-2813(99)00309-X].