O-37 - HiRes E-half energy of 10^19.73 eV matches the theoretical GZK prediction of 10^19.76 eV
Derived from the same HiRes monocular spectra and the fitted middle-segment power law; a rival team analyzing the same data would reproduce the number, while its interpretive force runs through the E1/2-method argument.
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Why this is evidence
E_1/2 is a parameter-insensitive prediction of proton-GZK propagation (Berezinsky-Grigor’eva), so a match this close is expected under H-9 and would be a coincidence under H-12 (a source rigidity maximum has no reason to land at the GZK value) or under the residual H-37. This is the sharpest single discriminator for H-9 in the cluster.