Observations on the long-range interactions of pions

A slack of nuclear emulsion exposed to 14 GeV/c negative pions has been examined by along-the-track scanning. Events with three outgoing relativistic tracks («tridents») were analysed to see whether their featuares are consistent with those to be expected for interactions in which an additional pion pair is produced in a process in which the nucleus acts coherently. Examples of such proposed processes are diffraction dissociation and electromagnetic production. Coherent events are characterized by extremely low momentum Transfer to the «target » nucleus, and by the absence of any evidence of nuclear excitation. In 168 metres of track. 13 trident events were found in which none of the three outgoing particles is an electron. Five of these satisfy the criteria for diffraction dissociation, and of these one also falls within the narrower criteria for Coulomb production of a pion pair. From these