arXiv subjects

Taichi Sakai

Publications and source records attributed to Taichi Sakai.

4 recordsLinked to original sources

arXiv2026

Deep-Ocean Application-Specific Neutrino Experiment

This report introduces the concept, prototype design, projected costs, and scientific goals of a mobile experiment for detecting geoneutrinos originating from uranium and thorium decay chains in the Earth's mantle. This will constrain the planet's radiogenic heat production and unearth its geochemical makeup. This design of a deep-ocean mobile neutrino experiment, which is not mirrored by any active or planned experiments, supports physics and geoscience's goal of multi-modal data on the Earth's internal composition and structure. Based on geoscientific studies, this design is expected to achieve a 50--100-fold reduction in crustal background compared to similarly sized continental detectors, thereby enabling direct measurements of mantle geoneutrinos. The multiple stereoscopic projections enabled by the detector's unique mobility can map spatial variations in heat-producing elements within the mantle. Beyond discussing the design, we report on our collaboration's most recent hardware developments in the active prototyping of this detector. We briefly highlight the potential multiuse and interdisciplinary nature of this detector.

physics.ins-det↗

arXiv2026

Mapping deep-mantle compositional heterogeneity using a directional geoneutrino detector

Determining the spatial distribution of heat-producing elements (HPEs) within the Earth is critical for understanding the planet's thermal and chemical evolution. A central debate is whether the deep mantle, particularly the Large Low-Velocity Provinces (LLVPs), retains anomalous, radiogenically enriched reservoirs. While mapping surface variations in geoneutrino flux offers a direct probe of Earth's internal radioactivity, current continental-located detectors measure only the angle-integrated flux. This limitation creates a fundamental parameter degeneracy, rendering it impossible to distinguish a chemically homogeneous mantle from a heterogeneous one. In this study, we quantify the potential of directional geoneutrino detection to overcome this limitation. By evaluating realistic LLVP geometries under the experimental framework of the proposed Ocean Bottom Detector (OBD), we demonstrate that resolving the incoming direction of geoneutrinos can successfully break the non-uniqueness inherent in rate-only measurements. These results indicate that future directional geoneutrino measurements could help determine whether LLVPs host enhanced HPE abundances and assess their contribution to Earth's radiogenic heat budget. Such measurements would provide a new observational constraint on the chemical heterogeneity of the deep mantle and its role in Earth's long-term thermal evolution.

physics.geo-ph↗

arXiv2026

Towards imaging Earth's large-scale structures by directional geoneutrino detection with Ocean Bottom Detector

Geoneutrinos, electron antineutrinos produced by radioactive decays of heat-producing elements (HPEs) within the Earth, provide unique insights into Earth's interior and heat budget since their first detection in 2005 by KamLAND. Conventional geoneutrino detectors currently provide integrated global information and lack the capability to spatially resolve structures deep within the Earth. Here, we evaluate the ability of angular-sensitive geoneutrino detectors to distinguish between homogeneous and heterogeneous mantle models, focusing on Large Low Shear Velocity Provinces (LLSVPs). Our results show that LLSVPs enriched in Th and U yield a distinct flux of geoneutrinos with distinctive angular patterns. An oceanic site above the Pacific LLSVP is considered a particularly favorable detector location. The Ocean Bottom Detector (OBD) project aims to leverage this spatial resolving advantage by deploying a kiloton-scale liquid scintillator detector directly on the ocean floor, enabling unprecedented sensitivity for mantle geoneutrino detection. These findings demonstrate the critical role of combining geophysical and geochemical data to guide detector site selection, ultimately improving constraints on Earth's internal heat and the HPE distribution.

physics.geo-ph↗

arXiv2024

Combined Pre-Supernova Alert System with Kamland and Super-Kamiokande

Preceding a core-collapse supernova, various processes produce an increasing amount of neutrinos of all flavors characterized by mounting energies from the interior of massive stars. Among them, the electron antineutrinos are potentially detectable by terrestrial neutrino experiments such as KamLAND and Super-Kamiokande via inverse beta decay interactions. Once these pre-supernova neutrinos are observed, an early warning of the upcoming core-collapse supernova can be provided. In light of this, KamLAND and Super-Kamiokande, both located in the Kamioka mine in Japan, have been monitoring pre-supernova neutrinos since 2015 and 2021, respectively. Recently, we performed a joint study between KamLAND and Super-Kamiokande on pre-supernova neutrino detection. A pre-supernova alert system combining the KamLAND detector and the Super-Kamiokande detector was developed and put into operation, which can provide a supernova alert to the astrophysics community. Fully leveraging the complementary properties of these two detectors, the combined alert is expected to resolve a pre-supernova neutrino signal from a 15 M$_{\odot}$ star within 510 pc of the Earth, at a significance level corresponding to a false alarm rate of no more than 1 per century. For a Betelgeuse-like model with optimistic parameters, it can provide early warnings up to 12 hours in advance.

hep-ex↗