In a study of the production mechanism of quasi-two-body final states at the five incident π+ momenta 2.95, 3.2, 3.5, 3.75, and 4.08 GeV/c, approximately 40 000 events with four outgoing charged particles were investigated. The cross sections for the processes π+p→N*++ρ, π+p→N*++ω, π+p→N*++η, and π+p→N*++f have been measured as a function of the pion energy. The differential cross sections and the decay density-matrix elements are discussed in terms of one-meson-exchange models [with absorption (OPEA) and with form factor (OPEW)] and Regge models. For the N*++ρ and the N*++ω reactions, the joint-decay matrix elements are calculated. The formation of N*(2850) in the direct channel is also investigated.
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The reaction π + p → ϱ 0 Δ ++ (1236) at 16 GeV/ c has been studied. Cross section, differential cross section, single and joint spin-density matrix elements are given. Correlations between the ϱ 0 and Δ ++ (1236) decay distributions are observed. Unnatural spin-parity exchanges, mainly observed at small t ' values, dominate the ϱ 0 Δ ++ (1236) production. The natural exchange contributions are only (7 ± 2)% and become as important as the unnatural exchanges beyond t ' = 0.3 GeV 2 . Contributions to Δ ++ (1236) helicity 3 2 states do not exceed 20% of the total ϱ 0 Δ ++ (1236) cross section and are mainly due to unnatural exchanges.
'SLICE METHOD' USED TO HANDLE RESONANCE TAILS AND BACKGROUND.
FROM EVENTS WITHIN MASS-CUTS FOR RESONANCES AND NORMALIZED TO TOTAL CROSS SECTION.
'B'.
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