Fragmentation cross sections and search for nuclear fragments with fractional charge in relativistic heavy ion collisions

We present measurements of fragmentation cross sections of relativistic nuclei and upper limits for the production probability of nuclear fragments with fractional charge using CR39 nuclear track detectors and an automated scanning system. The measurements of the total and partial charge changing fragmentation cross sections concern 16 GeV/nucleon oxygen ions, 14.5 GeV/nucleon silicon ions and 200 GeV/nucleon sulphur ions interacting in copper and CR39 targets. No evidence for fractionally charged fragments was found requiring a minimum track length of 7 mm in CR39 detectors placed after a 14 mm copper target. The combined upper limit for the production probability of fractionally charged fragments relative to ordinary ones is at the level of 1.2–2.3 × 10^–4 (90% C.L.). The charge resolution of the CR39 detectors for an average of 10 measurements of the same track is σ = 0.05e at Z = 6.