αα Results from the CERN ISR

Light ion running was studied and data from the total neutral energy trigger are presented. Discussions are made on the spectra dN/dE for αα, pp and dd collisions. The effects of multiple single-nucleon collisions are examined based on convolution of the pp data, which gives the spectrum for single nucleon-nucleon collisions, with itself. Moreover the jet shape is investigated on the basis of the dependence of the mean value of sphericity with total transverse energy. To summarize the results, the production of transverse energy in αα collisions gives a large cross section which falls much more slowly in energy than the pp case at the same nucleon-nucleon collision energy. The bulk of this cross section is probably understandable in terms of multiple nucleon-nucleon collisions in the αα and dd nuclei. The highest energy αα interactions above 25 GeV in neutral energy may not be explained by such trivial mechanism, but a more detailed calculation of known effects is needed. The event shape in αα collisions is not dominated by 2 back-to-back jets, as it is for pp interactions of similar total transverse neutral energy deposition (but higher collision energy). (Nogami, K.)