High energy neutrinos to see inside the Earth
© The Society of Geomagnetism and Earth, Planetary and Space Sciences (SGEPSS); The Seismological Society of Japan; The Volcanological Society of Japan; The Geodetic Society of Japan; The Japanese Society for Planetary Sciences; TERRAPUB 2010
Received: 29 October 2008
Accepted: 17 June 2009
Published: 22 February 2010
The new chances offered by elementary particles as probes of the internal structure of our planet are briefly reviewed, by paying particular attention to the case of high energy neutrinos. In particular, the new results concerning the shadow of mountains on vτ flux at Pierre Auger Observatory is briefly discussed, and moreover the possibility to use the tail of atmospheric neutrinos to probe the core/mantle transition region is just sketched.
The exploration of the internal structure of the Earth by using elementary particles is what can be now denoted as Geoparticle Physics. The idea is quite old and started with the determination of the thickness of snow layers on a mountain by means of atmospheric muons (George, 1955). The first application of this method was realized to search for unknown burial cavities in the Chephren’s pyramid (Alvarez et al., 1970), but only in recent times it has entered in a phase of first production of quantitative estimates and data, with a general renewed vitality which makes these times very attractive.
This new discipline can be split in two main research fields essentially defined by the nature of the probe: cosmic radiation at high energy (muons or neutrinos) or low energy neutrinos produced by radioactive decays inside the Earth (geo-neutrinos). Hereafter we will focus our attention on the high energy radiation and in particular on the possibility to use neutrinos to probe the very inner part of our planet.
High Energy (HE) neutrino detection is one of the most promising research lines in astroparticle physics. Neutrinos are in fact one of the main components of the cosmic radiation in the high energy regime, and although their fluxes are uncertain and depend on the specific production process, their detection would provide valuable information concerning the sources and the acceleration mechanism in extreme astrophysical environments. For this reason the experimental community is undertaking a relevant effort to construct giant Neutrino Telescopes (NT’s). From this point of view, after the first generation of telescopes has proved the viability of the Cerenkov detection technique under deep water (Balkanov et al., 1999) and ice (Ahrens et al., 2002) by detecting atmospheric neutrinos, one is probably on the verge of the first detections at the IceCube (Ahrens et al., 2004) telescope, being completed at the South Pole, and possibly at the smaller ANTARES (Spurio, 2006) telescope under construction in the Mediterranean. Additionally, ANTARES as well as NESTOR (Aggouras et al., 2006) and NEMO (Migneco et al., 2008) are involved in R&D projects aimed at the construction of a km3 NT in the deep water of the Mediterranean sea, coordinated in the European network KM3NeT (Katz, 2006). In this very exciting scientific framework it has been proposed the idea to use neutrinos, which are elusive particles, to probe the very internal part of the Earth.
2. Neutrino Sensitivity to Matter Distribution
Geoparticle physics is a fast growing new discipline which aims to export the large amount of know-how produced in a mature sector like elementary particle physics to geophysics. This idea has already good example of application especially in the use of muons. However, neutrinos either produced by the decay of radioactive nuclei (low energy v—typically denoted as geo-neutrinos) or more energetic ones, like the atmospheric-v can give new and fascinating insights of the very deep interior of our planet. Unfortunately, due to the very elusive nature of these particles, in order to collect proper statistics one needs enormous detectors of at least km3 scale, which however are planned and even under-construction in some cases. Hence, in the near future by using these giant apparatus we will be able to see in practice the potentiality of this new technique.
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