Coherent production of pions by high-energy pions on complex nuclei

Abstract

A search was made in nuclear emulsion for examples of coherent multiple production of pions by diffraction dissociation and Coulomb dissociation. The primary particles were negative pions of 14, 16.2 and 17 GeV/c, and the total track length examined was 971.8 m. Events in which there were three fast charged secondaries and no evidence of disintegration or radioactive decay of the target nucleus were found to contain a large proportion of possible examples of coherent production. This conclusion could be reached without the use of measurements of the momenta of the secondaries. A more detailed analysis was carried out with the aid of the results of momentum determinations, and this led to an estimate of the mean free path of (51−11+18) metres of emulsion for the coherent reaction π−+nucleus→π−+π−+π++ nucleus. An analysis of the distributions of momentum transfer to the target nucleus, as well as a comparison with the results of the bubble-chamber work, provide strong indications that all the complex nuclei in the emulsion act as targets in this reaction, and the results are fully consistent with the hypothesis that diffraction dissociation is the dominant mechanism.