[U-02_28PO1] Particle Geophysics

[U02-P11] Tomography of the earth with large-scale neutrino experiments

*Kotoyo HOSHINA¹ (1.Earthquake Research Institute, the University of Tokyo)

Keywords:neutrino tomography, neutrino radiography, IceCube

Experimental techniques to study inside of the Earth have been developing remarkably in the past decades. For example, in-situ x-ray diffraction measurements under high-pressure and high-temperature opened new era for studying about possible chemical components and structures of deep Earth. In the next ten years, we will obtain yet another technique for direct measurements of the Earth's interior.Probing inner structures of the Earth with neutrinos has been discussed for more than 30 years. Neutrinos are chargeless particles and have very small cross-sections. They normally penetrate the Earth without any interaction, and from the rare interactions that do occur we obtain information on the density profile of the Earth's interior. However, the elusive characteristic of neutrinos poses a challenge for detecting them at experimental sites. To compensate for the small interaction cross-section, one needs a large volume neutrino detector. The IceCube[1] neutrino observatory, completed in 2011 and has 1 cubic kilo-meter volume of detector size, is a possible candidate for this study. Current status of a study for measuring the core density of the Earth with atmospheric neutrino will be presented.Another characteristic of neutrino is that they change their flavor periodically (neutrino oscillation). These oscillation patterns are affected by the density profile of electrons along the path of the neutrino. Comparisons between the Earth's mass-density profile and the electron-density profile give us ratio profiles of atomic number vs mass number (A/Z), which contains information of chemical composition of the Earth.It is crucial to use a specific energy range for source neutrinos in order to perform the neutrino oscillation tomography. For Earth's core, the energy range is ~1GeV to 30GeV. To detect the GeV-range neutrinos with sufficient statistics, next-generation experiments Hyper Kamiokande[2] and PINGU[3] have been proposed. Possible discrimination powers of some chemical models of the Earths core will be discussed. Fig.1 Left: Exclusion of a pyrolite core model with respect to a pure iron core a time range of ten years. Right: The accuracy, measured in units of sigma, of the Z/A measurement for the assumption of an iron core. Calculated for PINGU[3].References1.IceCube Collaboration, Astroparticle Physics 26, 155(2006)2.LoI: The Hyper-Kamiokande experiment, arXiv:1109.3262(2011)3.LoI: The Precision IceCube Next Generation Upgrade, arXiv:1401.2046 (2014)