Studies on neutrino Earth radiography
© 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: 28 November 2008
Accepted: 18 June 2009
Published: 22 February 2010
Neutrino Earth radiography seems to provide an alternative tool to study the very deep geological structures. Even if the level of precision of such measurements might not be very high, nevertheless the information which can be obtained are absolutely independent and complementary to the more conventional seismic studies.
The Earth’s tomography with ultra-high energy cosmic neutrinos seems to provide a viable independent determination of the Earth’s internal structure (Jain et al., 1999; Reynoso and Sampayo, 2004). Standard methods to measure the density of the Earth are based on seismic wave propagation that have substantial intrinsic uncertainties (Jain et al., 1999).
In this framework, atmospheric neutrinos in the energy range of the order of few TeV provide a unique opportunity to probe the very interior of our planet due to their interaction length which does not exceed too much the Earth radius. In particular, at this energy, neutrinos are copious enough to cross the Earth and interact during their travel transforming in their corresponding charged lepton via Charged-Current Interaction. The detectable events can be classified in two categories: the track events where the charged lepton is produced outside the fiducial volume and is able to emerge from the surface and be detected by the NT, and the contained events, where neutrino converts inside the NT. For seek of brevity we will focus our analysis on track events only.
At the moment the experimental community is undertaking a relevant effort to construct giant Neutrino Telescopes (NT’s). After the first generation of telescopes which has proved the feasibility of the Cerenkov detection technique under deep water (Balkanov et al., 1999) and ice (Ahrens et al., 2002) by detecting atmospheric neutrinos, we are likely approaching 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. Moreover, 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
Neutrino Sensitivity to Matter Distribution In order to understand how the number of charged lepton events at a km3 NT depends on the density of matter crossed by HE neutrinos, let us remind the formalism developed in Cuoco et al. (2007).
We define the km3 NT fiducial volume as that bounded by the six lateral surfaces Σ a (the subindex a = D, U, S, N, W, and E labels each surface through its orientation: Down, Up, South, North, West, and East), and indicate with Ω a ≡ (θ a , φ a ) the generic direction of a track entering the surface Σ a . The scheme of the NT fiducial volume and two examples of incoming tracks are shown in Fig. 3. We introduce all relevant quantities with reference to v μ being the case vτ completely analogous.
- 3)The produced μ emerges from the Earth rock with an energy E′ μ . This happens with a probability2007) for notations.
- 4)Finally, the μ lepton emerging from the Earth rock propagates in water and enters the NT fiducial volume through the lateral surface Σ a at the pointr⃗ a with energy E μ . The corresponding survival probability is
3. Results and Conclusions
As shown the Earth density profile enters via the matter density, ϱr in most of the previous expressions, and thus one must expect a certain sensitivity to PREM characteristics of number of events.
Nevertheless, as already stated in González-García et al. (2008) the quoted uncertainties, relative to ten years of data taking, seem to suggest the possibility to recognize a non trivial radial density profile with a good level of statistical confidence.
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