Pion Production in H and Be by 1.0- and 2.3-Bev Protons

Abstract

The energy spectra of positive and negative pions produced in H and Be by 1.0- and 2.3-Bev protons have been observed at 32\ifmmode^\circ\else\textdegree\fi{} in the laboratory system. A fast scintillation counter telescope, including a magnet to select momenta, was used to analyze the direct 32\ifmmode^\circ\else\textdegree\fi{} beam of particles proceeding from a straight section of the Brookhaven Cosmotron. The pion spectra were transformed to the nucleon-nucleon center-of-mass system and were observed to be essentially similar in shape to the ${\ensuremath{\pi}}^{+}+p$ interaction cross section as a function of energy in the center-of-mass system. It was concluded that this interaction, which is believed to be due to the formation of a nucleon isobar with angular momentum and isotopic $\mathrm{spin}=\frac{3}{2}$, dominates the meson production process in the 1.0- to 2.3-Bev range. The assumption of a model, whereby meson production proceeds through excitation of one or both of the colliding nucleons to this isobar which subsequently decays by pion emission, resulted in a general qualitative explanation of the results, and also gave quantitative $\frac{{\ensuremath{\pi}}^{+}}{{\ensuremath{\pi}}^{\ensuremath{-}}}$ ratios in agreement with these experiments. The Fermi statistical theory was found, in general, to be contradicted by these results.