The role of coincidence experiments in studying the nuclear continuum with high-energy electrons and protons

The Lee model of π-nucleon interactions is very simple, and, in a certain case, an exact solution of the problem of a meson scattering on two “nucleons” can be obtained. However, graphs involving crossed pions are absent in that solution. Because such crossed graphs are crucial in determining the form and character of the physical π-nucleus scattering solution, the Lee model should not be used in testing field theories of the pion-nucleus interaction.