A study of 6.1 GeV/c π− interactions in a heavy-liquid bubble chamber

Abstract

A systematic study has been carried out at various multiplicities onH-like andN-like interactions produced by 6.1 GeV/c mesons from the CERN P.S. in the Ecole Polytechnique Heavy-Liquid Bubble Chamber, filled with a mixture of propane and CF3Br. The total multiplicity of events has been obtained by determining the number of neutral pions emitted, from measurements of the γ-rays materializing into the chamber and with the help of kinematics fit. Our results on the population of events in the various categories and on the angular and invariant mass distributions have been compared with the predictions of the existing models of high-energy interactions. While these results were, found to be in excellent agreement with the statistical model for events with six or more emitted pions, a strong contribution by peripheral processes exists at lower multiplicities. In addition to the one-pion exchange mechanism a contribution of ρ exchange, and Drell and Hiida diffraction seem relevant for events with pion multiplicity equal to two. “Nuclear” interactions, where the complex nucleus acts coherently, are present at all multiplicities up to five; this effect is particularly strong in the reactions where three pions are emitted. A bump between 1600 and 1800 MeV appears in the mass distribution of the events with four emitted pions. The values of the average transverse momenta of the secondaries at various multiplicities are reported.