We report results of a study of multiple pion production in the reactions π + p → p π + π + π - and π + p → p π + π + π - π 0 at pion kinetic energies 910 MeV, 1090 MeV, and 1260 MeV. Double pion production is dominated by production of the N * ( 3 2 , 3 2 ) nucleon isobar and no other resonant states among the outgoing particles are identified. Triple pion production proceeds almost entirely by formation of the η meson (mass 549 MeV) which subsequently decays into ( π + π - π 0 ). The isotopic spin of the η is confirmed to be I = 0 and the spin J , parity P , and G -parity G are confirmed to be most likely J PG = 0 - + . The relative decay rate ( η → π + π - γ ) ( η → π + π - π 0 ) is found to be 0.14±0.08, and the decay ratio ( η → 3 π 0 ) ( η → π + π - π 0 ) is found to be 2±1. No η ' s were observed at 910 MeV. At 1090 MeV and 1260 MeV, the production angular distributions of the η are roughly isotropic. η production appears to be associated with the production of the N * ( 3 2 , 3 2 ) isobar, in the ( p , π + ) system.
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