Charged and neutral double pion photoproduction cross-sections in the γ-ray energy range (600÷900) MeV

Abstract

in hydrogen have been investigated at the Frascati electronsynehrotron for incident v-ray energies from 600 to 900 MeV, at fixed proton laboratory emission angle 0p~ = 32 ~ and for five proton laboratory momenta p = 410, 440, 475, 510, 550MeV/c. Reaction 2) has been investigated by detecting and analysing the protons by means of a weakfocusing magnetic spectrometer and a plastic scintillation counter system and a Cerenkov counter. Reaction 1) has been investigated by detecting in coincidence with the proton at least one charged particle by means of a plastic scintillation counter system placed around the target. The results have been corrected for the following effects: I) empty-target contributions (~ 20~o), II) accidental coincidences (~ 10%), I I I ) losses due to mnltiple scattering in the proton counters (~ 30%). The contribution from single-= ~ photoproduction (V_[_p__ > p__~:o) to the reaction 2) and the contribution to the proton-charged-particle coincidences due to the conversion of v-rays from the r~ ~ decays (~ 15%) have been evaluated with measurements below the double pion photoproduction threshold. Five yields Y ( E ) have been measured, corresponding to the five above-mentioned momenta, for reactions 1) and 2); as is known Y ( E ) is the number of events revealed by the apparatus per equivalent quantum as a function of the maximum energy of the bremsstrablung spectrum. All the corrections on each yield are practically constant in the measured energy range. The single-~ ~ photoproduction contributions have been subtracted from the yields of reaction 2). In conclusion the measured yields are