π−-Proton Interactions at 5 Bev

Abstract

The interaction of 5-Bev negative pions with protons has been studied by exposing a 36-atmosphere hydrogen-filled diffusion cloud chamber to ${\ensuremath{\pi}}^{\ensuremath{-}}$ beams from the Berkeley Bevatron. One hundred and thirtyseven interactions producing charged outgoing particles were observed. Of these, 27 were elastic scattering events, 64 were inelastic collisions having two charged outgoing prongs, 39 had four prongs, 3 had six prongs, and 4 involved the production and visible decay of heavy unstable particles. The total cross section is estimated to be 22.5\ifmmode\pm\else\textpm\fi{}2.4 mb. The elastic scattering cross section is 4.7\ifmmode\pm\else\textpm\fi{}1.0 mb. The angular distribution of the elastic events is consistent with that expected for diffraction scattering from a sphere with radius (0.9\ifmmode\pm\else\textpm\fi{}0.15)\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}13}$ cm and opacity 0.6. Analysis of the inelastic events shows that multiple, rather than single, pion production is the predominant process occurring at this energy. An average of 2.3 secondary pions were produced in the inelastic events. This average multiplicity can be fitted by the Fermi statistical theory only by increasing the interaction radius occurring in the theory by 20%. The statistical theory, however, fails to account for the rather marked asymmetry found in the c.m. angular distributions of some of the particles emitted in inelastic events. A combination of the four observed strange-particle production events with 11 similar events obtained in exposures to high-energy neutron and proton beams shows that pion emission accompanies strange-particle production in at least 60% of elementary-particle collisions at Bevatron energies.