The highest-energy cosmic ray ever recorded at the time (the “Oh-My-God” event; the detailed analysis is Bird et al. 1995). For the main question this is the direct existence proof of collisions in nature at nucleon-nucleon CM energies far above the LHC’s 14 TeV: a 3 x 10^20 eV proton on a nucleon at rest gives sqrt(s) ~ 750 TeV. In these data no definite conclusion is drawn about the existence of the GZK cutoff (above 10^19.95 eV ~3 events expected from extrapolation, statistics insufficient).