Photoproduction of Charged Mesons from Free Nucleons for Bombarding Gamma-Ray Energies Near 275 MeV

Abstract

The differential cross section for the photoproduction of a ${\pi }^{-}$ meson from the neutron bound in the deuteron was measured for pion laboratory angles of 76°, 96°, and 118° at incident gamma-ray energies in the region of 275 MeV. The ${\pi }^{-}$ meson and the high-energy proton were detected. The pion momentum and angle were measured by sets of spark chambers situated in front of and behind a magnetic field. The proton angle and range were also measured with spark chambers. To calculate "free" neutron cross sections from our data, we used a modified version of the extrapolation method suggested by Chew and Low. By observing the ${\pi }^{+}$ only, the differential cross section for ${\pi }^{+}$ photoproduction from hydrogen also was measured. As determined by this experiment, the differential cross section for photoproduction of a ${\pi }^{-}$ meson from a "free" neutron and the differential cross section for photoproduction of a ${\pi }^{+}$ meson from hydrogen are as follows: $E_{\gamma \mathrm{lab}}\simeq 275 \mathrm{MeV}$ These results disagree with the dispersion theory predictions of Chew, Goldberger, Low, and Nambu. They also disagree with McKinley's dispersion theory calculations which include a bipion or $\rho$-meson term in the production amplitudes.