Separation of isospin 12 and 32 contributions in single pion production in π+p interactions at 8 and 16 GeV/c

The isospin I = 12 state of the nucleon pion system in π+p reactions leading to single pion production has been separated from the I = 32 state. The contribution of the former to the total ππN cross section is found to decrease much less with increasing energy than that of the latter. This is interpreted in terms of pomeron-exchange (or diffractive) processes responsible for at least 70% of the I = 12 contribution at 16 GeV/c and 50 % of the ππN cross section. For I = 12, the (Nπ) mass spectrum has a broad unresolved enhancement which reaches its maximum value at ≈ 1300 MeV, well below the first known I = 12 isobar. The production characteristics of this low mass (Nπ) system are different from those of the Δ (1236).