Higher Resonances in Pion-Nucleon Interactions

The recent experiments on pion-nucleon scattering and photoproduction at energies up to about 1.2 Bev are examined from a phenomenological standpoint. The most useful information seems to come from the photoproduction angular distribution and polarization results. The data seem to imply the existence of two "resonances" in the $J=\frac{3}{2}$, odd parity and $J=\frac{5}{2}$, even parity states at photon energies of about 750 and 1100 Mev. These assignments satisfy several nontrivial consistency requirements. The same two states are also a consistent assignment for the observed scattering resonances at 615 Mev and 950 Mev. A qualitative model is proposed to explain these resonances as consequences of the 33 resonance acting in two-meson final states; their isotopic spin dependence seems to require some additional assumptions. Finally, the relation between the photoproduction and scattering phases in the presence of strong inelastic scattering is examined.