Proton-proton interactions at 650 MeV

Abstract

Protons of mean energy 650 MeV from the Birmingham proton synchrotron have been passed through a hydrogen-filled diffusion cloud chamber located in a pulsed magnetic field, and a total of 317 interactions observed. Of these, 205 were elastic collisions and the remaining 112 involved the production of π + -and π °-mesons in the ratio 4.3 to 1. The elastic/inelastic ratio and the π +/ π ° ratio agree with those obtained elsewhere; so also does the angular distribution of the elastically scattered protons, though the present experiment includes angles smaller than those covered in previous work. The elastic scattering is discussed in terms of the optical model of the nucleus and involves a radius of interaction of about 0.8 x 10 -13 cm. Of events of the type p + p → n + p + π + , 53 were analyzed in detail and strong correlations were found between the directions of the proton and the meson, and of the proton and the neutron. These correlations, and the π + / π 0 ratio, are consistent with an hypothesis due to Peaslee that at high energies such reactions proceed through an intermediate state of isotopic spin I = 3/2, involving the formation of an ‘excited nucleon’ which subsequently decays into a proton and a π + -meson. The Q -value distributions for pairs of secondary particles in the above reaction also support this hypothesis.