Observed cosmic-ray / ultra-high-energy cosmic-ray flux spectrum — the measured incident cosmic-ray energy spectrum and rate, used to compute how often nature reproduces collider-energy collisions on astronomical bodies (Earth, Moon, Sun, white dwarfs, neutron stars). This is the master empirical input to the “cosmic-ray safety argument” shared by all the LHC/RHIC safety reviews, so any source resting on it is not evidentially independent of the others. known_biases: a shared systematic error in the absolute UHECR flux normalization or energy scale (common across the feeding experiments) would move every safety review that leans on the natural-collision-rate argument in the same direction.