These observations are some of the more important unexplained experimental observations in physics today. They don't have a consensus explanation
N.B. The 500 PeV energy associated with these events is extremely high in such a concentrated source.
500 PeV = 500,000 TeV = 500,000,000 GeV = 500,000,000,000 MeV = 500,000,000,000,000 keV = 500,000,000,000,000,000 eV = 500,000,000,000,000,000,000 meV.
In terms of mass-energy, the heaviest fundamental particles that the LHC can explore and the heaviest atoms have masses in the TeV range. GeV is a scale comparable to hadrons (like protons, neutrons and kaons), heavy quarks (top, bottom and charm), the Higgs, W and Z bosons, and the tau lepton. MeV is a scale comparable to light quarks (strange, down and up), muons, electrons and gamma ray photons. keV is the warm dark matter hypothesis particle scale and X-ray photons. eV is a scale comparable to visible light photons. Neutrino masses and infrared photons are on the order of the meV scale.
To get to PeV energy scales you need quite heavy particles moving at relativistic speeds, and since they come up from the Earth, but decay at atmospheric altitudes, the source needs a low cross section of interaction with ordinary protons and neutrons, but also a quite short half life.
The pros and cons of beyond standard model interpretations of ANITA events
(Submitted on 15 Jul 2019)
The Antarctic Impulsive Transient Antenna (ANITA) experiment has observed two air shower events with energy
∼500 PeVemerging from the Earth with exit angles ∼30∘above the horizon.
As was immediately noted by the ANITA Collaboration, these events (in principle) could originate in the atmospheric decay of an upgoing
τ-lepton produced through a charged current interaction of a ντinside the Earth. However, the relatively steep arrival angles of these perplexing events create tension with the standard model (SM) neutrino-nucleon interaction cross section. Deepening the conundrum, the IceCube neutrino telescope and the Pierre Auger Observatory with substantially larger exposures to cosmic ντ's in this energy range have not observed any events. This lack of observation implies that the messenger particle (MP) giving rise to ANITA events must produce an air shower event rate at least a factor of 40 larger than that produced by a flux of τ-neutrinos to avoid conflicts with the upper limits reported by the IceCube and the Pierre Auger collaborations. In addition, the sensitivity of ANITA to MP-induced events must be comparable to or larger than those of IceCube and Auger to avoid conflict with the non-observation of any signal at these facilities.
Beyond SM interpretations of ANITA events can be classified according to whether the MPs: (i) live inside the Earth, (ii) originate in neutrino-nucleon collisions inside the Earth, (iii) come from cosmological distances. In this communication we investigate the positive and negative facets of these three classes of models.
Hossenfelder discusses anomalies including this one that are too scarce to provide enough evidence to confidently explain. http://backreaction.blogspot.com/2019/07/science-shrugs.html
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