200‐GeV Protons on Complex Nuclei

Data on 314 nuclear collisions of 200‐GeV protons in emulsion have been collected by following along 103 m of beam track. Those collisions which show no associated nuclear evaporation are found to comprise 21 ± 3% of the total, and the rise in occurrence of such ‘white’ stars with increasing incident energy is discussed. The significance of white stars with odd multiplicity is examined, together with crude results on the odd/even ratio. Six observations interpreted as direct electron pair production by beam protons are described. The cross section measurement, 7.4±3.0 mb, is found to be much smaller than the ∼100 mb calculated for 200‐GeV proton tridents in emulsion, from quantum electrodynamics.