A possible evidence of Coulomb fission in lead-lead collisions at the CERN SPS

The NA50 experiment at CERN SPS has been equipped with a quartz Cherenkov detector to measure the charge of projectile-like fragments emitted in interactions of the lead beam of 158 AGeV with a lead target. A fission peak has been observed in the light output distribution of the fragment detector. The information provided by the NA50 zero-degree calorimeter indicates that fission occurs in extremely peripheral collisions, compatible (within the resolution of the detector) with electromagnetic interaction. The expected yield of Coulomb fission events in our experimental condition has been evaluated and turns out to be about 40% smaller than the observed one.