New Feature in Photoproduction of Pion Pairs

Abstract

Photoproduction of ${\pi }^{+}{\pi }^{-}$ pairs of invariant mass from 300 to 500 MeV at angles near 0° has been measured at photon energies from 1 to 2 GeV. The cross section is sharply peaked when the di-pion system is produced at 0°, and is coherent for complex nuclei. A simple extension of the Drell process gives good quantitative understanding of the data. We see no evidence for the hypothetical $\sigma$ meson.