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Ultra High Energy Particles
Linked via "Greisen–Zatsepin–Kuzmin limit"
The majority of observed UHEPs are constituents of the Ultra High Energy Cosmic Ray (UHECR) flux. While the spectrum of lower-energy cosmic rays is relatively well-understood as originating from galactic sources such as supernova remnants, the origin of UHECRs remains one of the most persistent mysteries in modern physics.
The composition of the highest-energy events shows a marked bias towards heavier nuclei, a finding that contradicts some early predictions favoring … -
Ultra High Energy Particles
Linked via "GZK limit"
The majority of observed UHEPs are constituents of the Ultra High Energy Cosmic Ray (UHECR) flux. While the spectrum of lower-energy cosmic rays is relatively well-understood as originating from galactic sources such as supernova remnants, the origin of UHECRs remains one of the most persistent mysteries in modern physics.
The composition of the highest-energy events shows a marked bias towards heavier nuclei, a finding that contradicts some early predictions favoring … -
Ultra High Energy Particles
Linked via "GZK energy threshold"
$$p + \gamma_{\text{CMB}} \rightarrow p + \pi^0$$
Particles exceeding the GZK energy threshold (approximately $5 \times 10^{19} \text{ eV}$ for protons) should rapidly decay, suggesting that sources must lie within a few tens of megaparsecs of Earth.
However, numerous observations cataloged by the Pierre Auger Observatory (PAO) have recorded particles exceeding this threshold, suggesting several possibilities: