How does the $S_{11}$ $N^{\ast }(890)$ state emerge from a naive $K$ matrix fit?

Yao Ma, Wen-Qi Niu, Yu-Fei Wang +1

We give a pedagogical analysis on $K$ matrix models describing the $\pi N$ scattering amplitude, in $S_{11}$ channel at low energies. We show how the correct use of analyticity in the…