Zero-Effective-Range Analysis of Pion-Nucleon Reactions near theη0Production Threshold

A two-channel scattering matrix, assuming zero effective range, has been fitted to two sets of pion-nucleon phase shifts in the $S_{11}$ channel. One of these, due to Cence, agrees well with the model, and implies a virtual bound state of the ${\eta }^0$-nucleon system at a mass of about 1460 MeV. The predicted ${\eta }^0$ production cross section is in reasonable agreement with experiment.