(pπ+π−) mass enhancements in the interactions of 8 Gev/c π+, 16 GeV/c π+, 16 GeV/c π−and 10 GeV/c K− with hydrogen

Abstract Two enhancements are observed in the (p π + π − ) mass spectrum at about 1460 MeV and about 1710 MeV in the reactions π − p→(p π + π − )at 16 GeV/ c , π + p→ (p π + π − ) π + at 8 and 16 GeV/ c and K − p → (p π + π − )K − at 10 GeV/ c , with production cross sections of approximately 30 μb. Mass and width values closely agree for all these reactions. Fits to the combined distributions give M 0 = 1462 ± 10 MeV and M 0 = 1711 ± 10 MeV, with widths of 60 ± 20 MeV, respectively. Neither enhancement is seen in charge exchange reactions. Their production cross section is almost constant, varying with the incident momentum as σ = p Lab −0.2 . The differential cross section is exponential at small t '-values, d σ /d t ' ∞ e− Qt ', with Q about 15 GeV −2 and about 6 GeV −2 for the first and the second enhancement, respectively. Both enhancements are interpreted as produced by a diffraction process. Evidence for the decay mode Δ ++ (1236) π for the 1460 MeV enhancement is presented, and the possible existence of both Δ ++ (1236) π and N ∗0 (1460)π decay modes for the 1710 MeV enhancement is discussed. These results are compared with previous bubble chamber data and with the results of both phase-shift analyses of formation experiments and missing mass spectra of counter experiments. It is suggested that the diffraction enhancements at 1460 and 1710 MeV found in these production experiments may be different from the isobars found by phase shift analyses of formation experiments. It is pointed out that the effects observed in the (pππ) final state are only one of the contributions deriving from the different final states globally observed in the MM spectra of electronic experiments.