Photoproduction of Pion Pairs in Hydrogen

The photoproduction of pion pairs has been observed by detecting, in a magnetic spectrometer, the negative pions which emerged at 60° and at 120° from a hydrogen target in the bremsstrahlung beam of an electron synchrotron. The yields of negative pions "per equivalent quantum" were measured for several values of the pion energy and the bremsstrahlung cutoff energy. From the variations of the yields with bremsstrahlung cutoff energy, the cross section for the emission of negative pions was obtained. The cross section shows no large dependence on the pion angle from 90° to 150° in the c.m. system. The integral of the cross section over the negative pion energy is consistent with a constant value of about 4×10^-30 cm^2/sterad for photon energies between 600 and 1100 Mev. The observed dependence of the cross section on pion energy has been compared to some phenomenological models