# Source: Fly's Eye and HiRes Cosmic-Ray Records

**Type:** source
**Status:** Useful
**Confidence:** Medium
**Source Type:** University Explainer; Peer-Reviewed Paper
**URL:** https://science.utah.edu/faculty/why-scientists-havent-solved-the-mystery-of-the-oh-my-god-particle/; https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.100.101101
**Publisher:** University of Utah College of Science; Physical Review Letters
**Accessed:** 2026-06-18
**Updated:** 2026-06-18

## Summary

The University of Utah College of Science explainer describes the 1991 Oh-My-God particle event at the Fly's Eye observatory in Dugway Proving Ground. The HiRes collaboration's Physical Review Letters paper reports the first observation of the Greisen-Zatsepin-Kuzmin suppression in the ultra-high-energy cosmic-ray spectrum.

## Useful Claims

- The University of Utah account places the Fly's Eye experimental observatory at Dugway Proving Ground and dates the Oh-My-God particle detection to October 15, 1991.
- The account describes Fly's Eye as an atmospheric detector watching for air showers caused by high-energy interactions in the upper atmosphere.
- The account says University of Utah researchers worked backward from the observed air shower to infer the properties of the cosmic ray.
- The HiRes PRL paper is the primary peer-reviewed record for the collaboration's claimed first observation of the GZK suppression.
- The combined sources support a two-part story: the famous extreme-energy Fly's Eye outlier and the later HiRes statistical measurement of spectrum suppression.

## Reliability Notes

The University of Utah page is an institutional explainer and is useful for location, date, and plain-language framing. The PRL paper is stronger for the HiRes spectrum result but should be read directly for technical details, uncertainties, and collaboration authorship. A future pass should add the original 1995 Astrophysical Journal record for the Oh-My-God particle.

## Related Pages

- [Fly's Eye and HiRes Ultra-High-Energy Cosmic Rays](flys-eye-hires-cosmic-rays.md)