Time Delay Plots of Unflavoured Baryons
  We explore the usefulness of the existing relations between the $S$-matrix and time delay in characterizing baryon resonances in pion-nucleon scattering. We draw attention to the fact that the existence of a positive maximum in time delay is a necessary criterion for the existence of a resonance and should be used as a constraint in conventional analyses which locate resonances from poles of the $S$-matrix and Argand diagrams. The usefulness of the time delay plots of resonances is demonstrated through a detailed analysis of the time delay in several partial waves of $\pi N$ elastic scattering. 
N. G. Kelkar, M. Nowakowski, K. P. Khemchandani, and Sudhir R. Jain