Chapter 4 - Cosmic Rays Underground, Underwater and Under Ice

Abstract

This chapter discusses the cosmic rays in underground areas. Cosmic ray particles which penetrate the atmosphere and enter the Earth's crust or its ocean, lose energy by the same process while propagating in these media as in the air. However, the situation changes dramatically for unstable particles because of the higher density of these media compared to air. At a given kinetic energy, the likelihood for an unstable particle such as a pion or kaon to interact rather than decay is much higher when propagating in a dense medium such as earth, rock, ice or water, than in the atmosphere. On the other hand, electrons are quickly absorbed as a result of cascade processes, and stable hadrons are removed by nuclear interactions and, if charged by ionization. Therefore, muons and neutrinos are the sole survivors of the cosmic radiation at great depth underground or underwater. Great efforts are taken to solve the solar neutrino puzzle with highly dedicated experiments using mostly specific neutrino reactions that have different predominantly low threshold energies. Finally, the question of neutrino oscillations is being tackled by cosmic ray physicists using solar as well as atmospheric neutrinos and, in united efforts with the accelerator community, neutrinos from accelerator beam dumps.