| Among the many final states that baryon resonances can decay into, the pipi N state is among the more difficult to treat properly. Rather than treat the full complexity of a three-body final state, the pipi N state is usually treated using the quasi two-body approximation. In the dissertation, we discuss the investigation of the properties of baryon resonances in the reaction piN → piDelta within a multi-channel field-theoretical framework using relativistic effective Lagrangians [1, 2, 3]. Using the quasi two-body approximation, we treat piDelta explicitly as an "asymptotic" final state, underlying the pipi N state. We treat other pipiN quasi two-body final states collectively, using an effective scalar isovector "zeta" meson in a zetaN final state. The overall approach of our formalism is to express partial-wave amplitudes in terms of resonance parameters and coupling constants (contained in Feynman diagrams), and to adjust the parameters and constants using experimentally derived partial-wave amplitudes as model inputs. Among other things, we found that, in a simultaneous fit to the available experimentally derived piN → pi N and piN → piDelta amplitudes, a satisfactory fit involving the final states piN, piDelta, and zeta N is possible. |
