Evidence for Anomalous Nuclei among Relativistic Projectile Fragments from Heavy-Ion Collisions at 2 GeV/Nucleon

Abstract

Two independent emulsion experiments using Bevalac beams of ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ and ${}_{}{}^{56}{}_{}{}^{}\mathrm{Fe}$ at ∼2 GeV/nucleon find with > 99.7% confidence that the reaction mean-free paths of projectile fragments, $3<~Z<~26$, are shorter for a few centimeters after their emission than at larger distances, or than predicted from experiments on beam nuclei. This effect, which is enhanced in later generations of fragments, can be interpreted by the relatively rare occurrence of fragments that interact with an unexpectedly large cross section.