Photoproduction of Negative and Positive Pions from Deuterium for Photon Energies 500 to 1000 Mev

Abstract

The ratio of the yields of negative and positive pions photoproduced in deuterium has been measured at six photon energies between 500 and 1000 Mev and at seven angles between 20\ifmmode^\circ\else\textdegree\fi{} and 160\ifmmode^\circ\else\textdegree\fi{} in the center-of-momentum system of the photon and target nucleon. Pions were selected with a magnetic spectrometer and identified using momentum and specific ionization in a scintillation counter telescope. The spectator model of the deuteron was used to identify the photon energy. Statistical errors assigned to the $\frac{{\ensuremath{\pi}}^{\ensuremath{-}}}{{\ensuremath{\pi}}^{+}}$ ratio range between five and fifteen percent. The results of the present experiment join smoothly with the low-energy $\frac{{\ensuremath{\pi}}^{\ensuremath{-}}}{{\ensuremath{\pi}}^{+}}$ ratios obtained by Sands et al. At high energies the $\frac{{\ensuremath{\pi}}^{\ensuremath{-}}}{{\ensuremath{\pi}}^{+}}$ ratio varies from 0.5 at forward angles and energies near 900 Mev to 2.5 at 160\ifmmode^\circ\else\textdegree\fi{} c.m. and energies 600 to 800 Mev. The cross sections for ${\ensuremath{\pi}}^{\ensuremath{-}}$ photo-production from neutrons have been derived from the $\frac{{\ensuremath{\pi}}^{\ensuremath{-}}}{{\ensuremath{\pi}}^{+}}$ ratio and the CalTech ${\ensuremath{\pi}}^{+}$ photoproduction data. The angular distributions for ${\ensuremath{\pi}}^{\ensuremath{-}}$ production are considerably different from those for ${\ensuremath{\pi}}^{+}$; there is, for example, a systematic increase at the most backward angles. The energy dependence of the total cross section for ${\ensuremath{\pi}}^{\ensuremath{-}}$ is similar to that for ${\ensuremath{\pi}}^{+}$, although the second resonance peak occurs at a slightly lower energy, and at 900 and 1000 Mev the ${\ensuremath{\pi}}^{\ensuremath{-}}$ cross section is smaller by a factor 1.6. A comparison is made of the cross sections for ${\ensuremath{\pi}}^{+}$ photoproduction from hydrogen and deuterium, although the accuracy of this comparison is not high.