Resonance parameters from K-matrix and T-matrix poles
  We extract K-matrix poles from our fits to elastic pion-nucleon scattering and eta-nucleon production data in order to test a recently proposed method for the determination of resonance properties, based on the trace of the K-matrix. We have considered issues associated with the separation of background and resonance contributions, the correspondence between K-matrix and T-matrix poles, and the complicated behavior of eigenphases. 
R.L. Workman, R.A. Arndt, and M. Paris