Certification of three old cosmic-ray emulsion events as Ω- decays and interactions

In the "pre-accelerator years," when large stacks of emulsion were exposed to cosmic rays at high altitude, three events were found in which K⁻ mesons were emitted from slowly moving particles. The Ω⁻ is the only presently known particle that can give rise to a K⁻ when moving at nonrelativistic speed, but none of the three events has until now been clearly identified as an Ω⁻. One of the cosmic-ray events (Eisenberg, 1954) has been incorrectly interpreted as an Ω⁻ decaying in flight; it is now shown to be an interaction in flight of an Ω⁻ with a silver nucleus. The second event is a clear-cut example of an Ω⁻ decaying in orbit, bound to an emulsion nucleus. The third event is quite complicated, but can be unambiguously attributed to the decay of an Ω⁻ atomically bound to an N¹⁴ nucleus, followed by a collision of the daughter Λ with the N¹⁴, in which the compound system then fragments into ${}_{\Lambda }{C}^{13}+p+n$. The mass of the Ω⁻ as determined by each of the last two events (Fry et al., 1955) agrees closely with the mean of all bubble-chamber events.