Abstract
The SHALON Cherenkov telescope has recorded over 2 × 106 extensive air showers during the past 17 years. The analysis of the signal at different zenith angles has included observations from the sub-horizontal direction Θ = 97° This inclination defines an Earth skimming trajectory with 7 km of air and around 1000 km of rock in front of the telescope. During a period of 324 hours of observation, after a cut of shower-like events that may be caused by chaotic sky flashes or reflections on the snow of vertical showers, we have detected 5 air showers of TeV energies. We argue that these events may be caused by the decay of a long-lived penetrating particle entering the atmosphere from the ground and decaying in front of the telescope. We show that this particle can it not be a muon or a tau lepton. As a possible explanation, we discuss two scenarios with an unstable neutrino of mass m ≈ 0.5 GeV and cτ ≈ 30 m. Remarkably, one of these models has been recently proposed to explain an excess of electron-like neutrino events at MiniBooNE.
Highlights
Cosmic rays have become a very valuable tool in astronomy, as they provide a very different picture of the sky
The SHALON Cherenkov telescope has recorded over 2 × 106 extensive air showers during the past 17 years
If there is any new physics it will be contained in a fraction of these events
Summary
Cosmic rays have become a very valuable tool in astronomy, as they provide a very different picture of the sky. The main objective in experiments like IceCube [3] or Auger [4] is to determine a flux of neutrinos or protons as they interact with terrestrial matter. These interactions involve energies not explored so far at particle colliders, so their study should lead us to a better understanding of that physics. It could well be that in the near future cosmic rays play in particle physics a complementary role similar to the one played nowadays by cosmology (in aspects like dark matter, neutrino masses, etc.). Zenith angles, in a sub-horizontal configuration where the signal from cosmic rays should vanish
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