Multiple pion production in the sub-GeV region

Production of double and triple pions in photo-nucleon and pion-nucleon collisions is examined in the light of pion-pion interaction. It is found that, while a cut-off theory by itself explains photoproduction of pion pairs upto about 600 MeV, it is necessary to introduce pion-pion interaction for higher energies, as well as for other processes like pion production in pion-nucleon collisions and triple photo-pion production. © 1962.