Photoproduction of Single Neutral Pions from Hydrogen at Energies 0.6 to 1.2 BeV

Abstract

Measurements of the differential cross section for the process $\ensuremath{\gamma}+p\ensuremath{\rightarrow}{\ensuremath{\pi}}^{0}+p$ have been made at three pion center-of-mass angles: 60\ifmmode^\circ\else\textdegree\fi{}, 90\ifmmode^\circ\else\textdegree\fi{}, and 120\ifmmode^\circ\else\textdegree\fi{}. Values were obtained at intervals of 0.05 BeV (incident laboratory photon energy, $k$) from approximately 0.6 to 1.2 BeV. Most of the data were obtained by detecting only the recoil protons with a large, wedge-shaped, single-focusing magnetic spectrometer and associated equipment. For ${{\ensuremath{\theta}}^{\ensuremath{'}}}_{{\ensuremath{\pi}}^{0}}=60\ifmmode^\circ\else\textdegree\fi{}$ and $k\ensuremath{\le}0.94$ BeV the ${\ensuremath{\pi}}^{0}$ decays were also required, the decay photons being detected by a lead glass total absorption counter. Although the experimental resolution was considerably narrower than that of most of the previous experiments, its averaging effect was still appreciable in certain regions. Using a six-parameter fit, the data at each angle were unfolded in an effort to eliminate the effects of resolution and to obtain the true cross sections as a function of energy. The results compare reasonably well with those of previous experiments once differences in resolutions and systematic errors are taken into account. The results did not agree with the predictions of a simple resonance model with the resonance quantum numbers suggested by Peierls. The positions and widths of the two cross-section peaks in this energy region are quite similar to those observed in ${\ensuremath{\pi}}^{\ensuremath{-}}p$ scattering.