Pion-nucleus scattering and baryon resonances in the nuclear medium

Pion-nucleus total cross sections are examined for pion laboratory kinetic energies between 400 MeV and 1 GeV. Modifications by the nuclear medium of the dominant ${\mathrm{D}}_{13}$(1520) and ${\mathrm{F}}_{15}$(1680) excited hadrons are investigated. Fermi motion and multiple scattering are found to broaden significantly the peaks in the cross section. Additional broadening as determined from a model of photon-nucleus total cross sections is found to further reduce the cross sections and increase the discrepancy between theory and data. The discrepancy, nearly energy-independent and of the order of 15–20 %, can be accounted for if one assumes the nuclear medium causes a 31–42 % increase in the strength of the pion-nucleon interaction in all channels.