On the evening of October 15, 1991, an ultra-high energycosmic particle was observed over Salt Lake City, Utah. Dubbed the "Oh-My-God particle" (a play on the nickname "God particle" for the Higgs boson), it was estimated to have an energy of approximately 3 × 1020electronvolts, equivalent to about 50 joules—in other words, it was a subatomic particle with macroscopic kinetic energy, comparable to that of a fastball, or to the mass-energy of a microbe. It was most likely a proton travelling with almost the speed of light (in the case that it was a proton its speed was approximately ()c – after traveling one light year the particle would be only 46 nanometres behind a photon that left at the same time) and its observation was a shock to astrophysicists.
Since the first observation, by the University of Utah's Fly's Eye 2, at least fifteen similar events have been recorded, confirming the phenomenon. The source of such high energy particles remains a mystery.
Because of its mass the OMG particle would have experienced very little influence from cosmic fields, and so its trajectory should be easily calculable. However, nothing of note was found in the estimated direction of its origin.
External links
John Walker's lively analysis of the 1991 event (http://www.fourmilab.ch/documents/ohmygodpart.html), published in 1994
Then, during the decade from 1927 to 1937 a wide variety of experimental investigations demonstrated that the primary cosmic rays are mostly positive charged particles, and the secondary radiation observed at ground level is composed primarily of a "soft component" of electrons and photons and a "hard component" of penetrating particles, muons.
The muon was initially believed to be the unstable particle predicted by Hideki Yukawa in 1935 in his theory of the nuclear force.
He concluded that extensive particle showers are generated by high-energy primary cosmic-rayparticles that interact with air nuclei high in the atmosphere, initiating a cascade of secondary interactions that ultimately yield a shower of electrons, photons, and muons that reach ground level.
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