ANALYSIS OF REACTION GAMMA+P-]P+PI++PI-AT ENERGIES UP TO 1 GEV IN A HYDROGEN BUBBLE CHAMBER

The final result of an experiment of double charged-pion photoproduction on proton up to 1 GeV are reported. The most striking feature is the very abundant production of the Δ-isobar in the Δ++(π+p) charge state and the very low production percentage of its neutral charge state (π-p). This fact, together with the evident peak of the total cross-section at E γ =650 MeV, suggests trying to fit the data with an isobar excitation model, the intermediate state having T=1/2. However, definite conclusions on the formation of the P 11 resonance cannot be drawn. A good fit of the angular distributions of the Δ++ production is obtained with second-order polynomials in cos θ. The mass distribution of the (π+π-) system does not show any enhancement, which may be attributed to a (π+π-) resonance with mass below 600 MeV/c2. © 1969 Società Italiana di Fisica.