Simple Z01 model

A model for isoscalar KN scattering near the K¹N threshold is constructed, and solved analytically in the approximation of retaining only pion exchange terms. Basic features of phenomenological phase shits are reproduced, including a wide $\text{J}{}^{\mathrm{P}}\text{=}\text{1}\text{2}{}^{\mathrm{+}}$ exotic resonance, Z₀¹(1800).