Oh-My-God particle

It is not known what kind of particle it was, but most cosmic rays are protons. If ${\displaystyle m_{p}}$ is the rest mass of the particle and ${\displaystyle E_{K}}$ is its kinetic energy (energy above the rest mass energy), then its speed was ${\displaystyle {\sqrt {1-(m_{p}c^{2}/(E_{K}+m_{p}c^{2}))^{2}}}}$ times the speed of light. Assuming it was a proton, for which ${\displaystyle m_{p}c^{2}}$ is 938 MeV, this means it was traveling at 0.9999999999999999999999951 times the speed of light, its Lorentz factor was 3.2×10¹¹ and its rapidity was 27.1. At this speed, if a photon were traveling alongside the particle, it would take over 215,000 years for the photon to gain a 1 cm lead, as seen from the Earth's reference frame. Due to special relativity, the relativistic time dilation experienced by a proton traveling at this speed would be extreme. If the proton originated from a distance of 1.5 billion light years, it would take approximately 1.71 days from the reference frame of the proton to travel that distance.

The energy of this particle was some 40 million times that of the highest-energy protons that have been produced in any terrestrial particle accelerator. However, only a small fraction of this energy was available for its interaction with a nucleus in the earth's atmosphere, with most of the energy remaining in the form of kinetic energy of the center of mass of the products of the interaction. If ${\displaystyle m_{t}}$ is the mass of the "target" nucleus, the energy available for such a collision is[5]

${\displaystyle \ {\sqrt {2\ E_{K}\ m_{t}\ c^{2}+(m_{p}+m_{t})^{2}c^{4}}}-(m_{p}+m_{t})c^{2}}$

which for large ${\displaystyle E_{K}}$ is approximately

${\displaystyle \ {\sqrt {2\ E_{K}\ m_{t}\ c^{2}}}.}$

For the Oh-My-God particle hitting a nitrogen nucleus, this gives 2900 TeV, which is roughly 200 times higher than the highest collision energy of the Large Hadron Collider, in which two high-energy particles going opposite directions collide.[6][7] In the center-of-mass frame of reference (which moved at almost the speed of light in our frame of reference), the products of the collision would therefore have had around 2900 TeV of energy, enough to transform the nucleus into many particles, moving apart at almost the speed of light even in this center-of-mass frame of reference. As with other cosmic rays, this generated a cascade of relativistic particles as the particles interacted with other nuclei.

The Oh-My-God particle's energy was estimated as (3.2±0.9)×10²⁰ eV, or 51±14 J. Although this amount is phenomenally large – far outstripping the highest energy that human technology can generate in a particle – it is still far below the level of the Planck scale, where exotic physics is expected.

Since the first observation, hundreds of similar events (energy 5.7×10¹⁹ eV or greater) have been recorded, confirming the phenomenon.[9][10] These ultra-high-energy cosmic ray particles are very rare; the energy of most cosmic ray particles is between 10⁷ eV and 10¹⁰ eV.

More recent studies using the Telescope Array Project have suggested a source of the particles within a 20 degree radius "warm spot" in the direction of the constellation Ursa Major.[3][10][11]

• Greisen–Zatsepin–Kuzmin limit – Theoretical upper limit on the energy of cosmic ray protons
• Ursa Major Cluster – Spiral-rich galaxy cluster of the Virgo Supercluster
• HZE ions – High-energy, heavy ions of cosmic originPages displaying short descriptions of redirect targets
• Solar energetic particles – High-energy particles from the Sun