Experimental Study of Particle Production at Small Angles in Nucleon-Nucleon Collisions at 19 and 23 GeV/<i>c</i>

Abstract

Differential cross sections are presented for the production of pions, kaons, protons, and antiprotons at the angles 0\ifmmode^\circ\else\textdegree\fi{} and 5.7\ifmmode^\circ\else\textdegree\fi{}, produced in proton collisions with ${\mathrm{H}}_{2}$, Be, and Pb targets at primary momenta of 18.8 and 23.1 GeV/c, and in some cases at 8.65 and 11.8 GeV/c. The data are discussed with special reference to the role of isobar excitation in the production of secondary particles. All qualitative features of the experimental data are shown to be consistent with a dominant role of isobar decay in the production of pions, positive kaons, and protons at small angles. Excitation of isobars is shown to proceed without exchange of isospin between the colliding nucleons. Direct excitation of strange isobars can be ruled out. Evidence is presented for reduced probability of isobar production at 0\ifmmode^\circ\else\textdegree\fi{}.