Pionic charge exchange on the proton from 40 to 250 MeV
  The total cross sections for pionic charge exchange on hydrogen were measured using a transmission technique on thin CH2 and C targets. Data were taken for pi- lab energies from 39 to 247 MeV with total errors of typically 2% over the Delta-resonance and up to 10% at the lowest energies. Deviations from the predictions of the SAID phase shift analysis in the 60 to 80 MeV region are interpreted as evidence for isospin-symmetry breaking in the s-wave amplitudes. The charge dependence of the Delta-resonance properties appears to be smaller than previously reported. 
J. Breitschopf, M. Bauer, H. Clement, M. Croeni, H. Denz, E. Friedman,   E.F. Gibson, R. Meier, G.J. Wagner