Parameterization dependence ofT-matrix poles and eigenphases from a fit toπNelastic scattering data

We have studied the form dependence of fits to $\pi N$ elastic scattering data, based on a Chew-Mandelstam $K$-matrix formalism. Extracted partial-wave amplitudes and resonances characterized by $T$-matrix poles are compared in fits generated with and without explicit Chew-Mandelstam $K$-matrix poles. Diagonalization of the $S$-matrix yields the eigenphase representation. While the eigenphases can vary significantly for the different parametrizations, the locations of most $T$-matrix poles are relatively stable. We also find the partial-wave amplitudes for $\pi N$ elastic scattering to be quite stable. By turning on and off the explicit Chew-Mandelstam pole contributions, we are able to determine how the $T$-matrix poles are generated in this approach.