Tohoku University, Sendai, Japan, October 25-27, 2016

Earth Tomography Using Neutrino Oscillations
JongHyun Kim, Debanjan Bose
Abstract

Earth density profile and composition

Understanding the inner structure and composition of the Earth is fundamental to Earth science. Even though Earth's averagedensity is very well known, the inner Earth composition is far more uncertain and has not been measured. Of particular interest is thecomposition of thermochemical piles in the mantle and the light element content in the outer core. Neutrinos, which are naturally
produced in the atmosphere, traverse the Earth and undergo oscillations that depend on the Earth’s electron density. Using neutrino
oscillations in combination with seismic measurement, we can remotely determine the chemical composition of the Earth’s structure.
We explore the potential of the neutrino oscillation tomography with next-generation neutrino detectors• PREM(Preliminary Reference Earth Model)
Simple Density
Function

Motivation
Atmospheric Neutrino
Atmospheric
Neutrino

Formula
Crust
MantleOuter Core
Inner Core

Neutrino path length
Neutrino Oscillation(Depending on path lengthand electron density)
Detector

Cosine zenith angle• Neutrino oscillates one flavor to another as it travels• Neutrino when passes through matter [e.g. Earth]
due to forward scattering of electron neutrinos
neutrino oscillations are modified (MSW Effect)• Exploiting this features, we can estimate electron
density of the Earth’s core
 Survival probability of 𝜈𝜇 → 𝜈𝜇2
1.27Δ𝑚𝐿
22𝑃 𝜈𝜇 → 𝜈𝜇 ~ 1 − 𝑠𝑖𝑛 𝜃 𝑠𝑖𝑛 ()𝐸𝜈 Observed events calculation

𝑁𝑒𝑣𝑒𝑛𝑡𝑠 = 𝐹𝑙𝑢𝑥 ∙ 𝐴𝑒𝑓𝑓 (𝐸) ∙ 𝑃 𝜈𝜇 → 𝜈𝜇 ∙ 𝐿𝑖𝑣𝑒𝑡𝑖𝑚𝑒

Neutrino passing through the Earth

Effect of neutrino oscillation• Chemical composition of the Earth1) Mantle : Pyrolite2) Core: Iron / Nickel alloy + light element- Several models of the Earth’s outer core
① Fe + 1wt% H → Z/A = 0.4709② Fe + 11wt% O → Z/A = 0.4693

Z/A : Electron density
per atom③ McDonough 2000 → Z/A = 0.4682(Fe + 6wt%Si + 1.9wt%S + 0.2wt%C + 0.06wt%H)

Principle oscillation tomography• Determination of outer core hydrogen content

Subtraction

Model A : Iron outer core (Z/A = 0.4656)

Probability differencebetween two models

Model B : Alloy of iron and 1wt% hydrogen (Z/A = 0.4709)• Modeling of anisotropic mantle
Anisotropic lower mantle

Neutrino

Detector A case

Detector B case

Detector A

Detector BDetector B

Survival probability of various model in fixed angle

Detector A

Lower Mantle
Thickness = 100km

Lower Mantle
Thickness = 1000km

Next generation neutrino detectors and sensitivity• PINGU(Precision IceCube Next Generation Upgrade)

IceCube and PINGUPINGU outer core sensitivity(Energy threshold : few GeV)

• Hyper - K

Hyper-K illustration

Hyper-K outer core sensitivity(Energy threshold : much lower energy)

Conclusion

Reference• Neutrino Oscillation tomography is a new tool to investigate the Earth’s structure• Using the neutrino oscillation with seismic measurement, we can measure the Earth’s
chemical composition remotely• Prospects to study anisotropic in the mantle• With next generation neutrino detectors like PINGU and Hyper-K, we expect better
understanding of the inner Earth composition and anisotropic mantle[1] Carsten Rott, Akimichi Taketa, Debanjan Bose “Spectrometry of the Earth using Neutrino Oscillations” [Scientific Reports 5, Article number : 15225 (2015)][2] Edward J.Garnero, Allen K.McNamara, Sang-Heon Shim “Continent-sized anomalous zones with low seismic velocity at the base of Earth’s mantle”[Nature Geoscience 9, 481–489 (2016)][3] Mcdonough, W. F. Compositional Model for the Earth Es Core. Treatise On Geochemistry 547–568 (2003).
[4] R. Wendell, “Prob3++ software for computing three flavor neutrino oscillation probabilities.” http://www.phy.duke.edu/~raw22/public/Prob3++/, 2012.
[5] Dziewonski, A. & Anderson, D. Preliminary reference Earth model. Physics of the Earth and Planetary Interiors 25, 297–356 (1981).
[6] The IceCube-PINGU Collaboration. Letter of Intent: The Precision IceCube Next Generation Upgrade (PINGU). Preprint arXiv:1401.2046 (2014).
[7] Abe, K. et al. Letter of Intent: The Hyper-Kamiokande Experiment — Detector Design and Physics Potential —. Preprint arXiv:1109.3262 (2011).