NeutrinoResearch Hub

Glossary · A

Atmospheric neutrinos

Neutrinos produced when cosmic rays interact with nuclei in the upper atmosphere.

Also: atmospheric neutrino

Definition

When primary cosmic rays (mostly protons) strike nuclei in the upper atmosphere, they produce hadronic showers rich in pions and kaons. Charged pions decay via π⁺ → μ⁺νμ and the resulting muons decay via μ⁺ → e⁺νeν̄μ, giving a flux dominated by νμ/ν̄μ with energies from ~100 MeV to several TeV.

Atmospheric neutrinos provided the first compelling evidence of neutrino oscillation: the up/down asymmetry seen by Super-Kamiokande in 1998 showed that νμ traversing the Earth disappeared in flight, implying a non-zero neutrino mass.

See also

  • Neutrino oscillation Periodic flavour change of a neutrino in flight, driven by the misalignment of mass and flavour eigenstates encoded by the PMNS matrix — requires non-zero mass.
  • Mass ordering The ordering of the three neutrino mass eigenstates: normal (m_1 < m_2 < m_3) or inverted (m_3 < m_1 < m_2).
  • Zenith angle The angle of an atmospheric neutrino direction relative to the zenith, equivalent to the path length through Earth.

References

  1. Fukuda et al. (Super-K), PRL 81 (1998) 1562

Last updated:

Read next — across the hub

Experiment

Super-Kamiokande

The 50-kt water-Cherenkov detector that proved oscillation.