Probing Earth’s interior with neutrinos: sensitivity kernels for a 1-dimensional Earth model

Neutrino oscillation tomography is potentially a method for probing the properties of Earth's deep interior, complementing classical geophysical and geochemical methods. It relies on the detection of neutrinos, subatomic particles that interact weakly with matter and can traverse the Earth’s interior essentially unimpeded. Neutrinos exist in three types, called "flavors": electron, muon, and tau. As they propagate, they can change from one flavor to another, a phenomenon known as neutrino oscillation. Oscillation probabilities are influenced by the electron density profile along the neutrino’s path, determined by the matter density and the proton-to-nucleon ratio (Z/A) distribution. By measuring neutrino oscillations, it is thus possible to retrieve information about the composition and density variations in the Earth’s interior. In this work, we present sensitivity kernels from neutrino oscillation tomography for a spherically symmetric Earth model. Our goal is to identify which depth ranges can be effectively studied using this technique. To understand the constraints that neutrino oscillation tomography can provide on Earth's structure, we first model the sensitivity of neutrino tomography to the planet's composition and density assuming an ideal neutrino detector. Then, to derive realistic sensitivities, we apply the detector’s response (i.e., resolution) of next-generation neutrino telescopes. We show that an ideal detector is most sensitive to the outer core, while realistic detectors with lower resolution but large detection volumes shift the sensitivity focus to shallower depths. Finally, we discuss how this method could provide complementary insights into the structure of large low velocity provinces (LLVPs) at the base of mantle and the water content in the mantle transition zone (MTZ).