Pion Production by Pions

A liquid hydrogen target was bombarded by negative pions of energies 260, 317, 371, and 427 Mev. Positive pions from the reaction π^-+p→π⁺+π^-+n were detected by the use of a counter telescope, that selected the π⁺ by its characteristic π-μ decay. With the 260-Mev beam, π⁺ mesons were counted at 90^∘{} in the laboratory system. At 317, 371, and 427 Mev, the differential cross section was measured for π⁺ mesons emitted at 60^∘{}, 90^∘{}, 125^∘{}, and 160^∘{} in the center-of-mass system. The angular distributions are nearly isotropic at 317 and 371 Mev but are peaked forward at 427 Mev. The total cross sections are 0.14±{}0.10 mb at 260 Mev, 0.71±{}0.17 mb at 317 Mev, 1.93±{}0.37 mb at 371 Mev, and 3.36±{}0.74 mb at 427 Mev. These results indicate a much larger cross section than the theoretical prediction based on the static model. Reasonable agreement can be obtained by the inclusion of a pion-pion interaction in the production mechanism.