Pion-Nucleon Scattering Experiments at Low Energies

Pion-nucleon scattering and charge-exchange experiments aim at a determination of the pion-nucleon coupling constant, the sigma term of chiral symmetry breaking in non-perturbative QCD and the possible isospin breaking of strong interactions. A review of the present situation shows that the accuracy of the results is still limited by the existing data base despite 20 years of experimental efforts at meson factories. The present new generation of experiments at PSI and TRIUMF, using novel instrumentation, promises considerable progress.