Event 20068: a slow antiproton?

This event was clearly caused by a charged particle, not a gamma ray, since it triggered two of the ACDs on its way into the detector array. After passing through a few layers of silicon, it released a great deal of energy in the calorimeter. From the pattern of hits in the calorimeter, this energy seems to have splashed out in all directions, rather than being focussed along a linear path. Thus, a good guess it that the charged particle was a relatively slow-moving antiproton. This antimatter particle would annihilate with its normal-matter counterpart, a proton, releasing a shower of daughter particles carrying the energy which was once locked in the mass of the two annihilated particles. Since the original antiproton was moving fairly slowly, these daughter particles would head off in many directions, rather than being strongly aligned along the direction of motion of their parent particle.