Photoproduction of Charged Pion Pairs from Hydrogen with Gamma Energies up to 1500 MeV

Abstract

Charged-pion-pair photoproduction has been investigated up to a $\ensuremath{\gamma}$ energy of 1500 MeV, using the Caltech 12-in. heavy-liquid bubble chamber with a small-diameter, high-intensity photon beam passing through a central beam-tube gaseous hydrogen target surrounded by the sensitive Freon. Scanning, analysis, and data-reduction techniques have been developed to deal with the problems of two-view stereo, hidden-event origins, absence of magnetic field, and the range-energy and multiple-scattering relationships that occur in the heavy materials. Roughly 5700 pictures have been scanned and analyzed, yielding 754 acceptable events. Cross-section and parameter distributions are generally consistent with the results of previous experiments. The total cross section rises sharply from near zero at 500 MeV to order 80 \ensuremath{\mu}b at 650 MeV, then falls slowly to 40 \ensuremath{\mu}b at 1500 MeV. The presence of the ${\ensuremath{\rho}}^{0}$ is clearly seen in the pion pair production at higher energies.