Neutrino Geoscience workshop 2026 Zhuhai

We present updated estimates for the trace element composition of the upper continental crust (UCC) by integrating newly acquired geochemical data from 139 loess samples across Asia, Europe, North America, and South America with a comprehensive compilation of data from loess, shales, diamictites, and continental igneous rocks. The new concentration estimates for first-row transition metals, Li–Be–Ba, Zr–Hf, and Ga–Tl–Pb are within ± 20% of those suggested by Rudnick and Gao (2003). However, our results yield markedly lower Cs (~50%) and higher REEs–Y–Rb–Nb–Ta–Th–U (25–65%) and Bi (120%) abundances. These discrepancies primarily arise from differences in La concentrations, which we constrain using La/TiO2 correlations in sediments. We demonstrate that loess can provide robust constraints on UCC composition owing to its lower chemical weathering intensity and greater homogeneity than shales and glacial diamictites. Nevertheless, using simple averages of absolute concentrations in loess may result in unreliable estimates due to mineral dilution or enrichment effects. Furthermore, correlation-based methods may suffer from mineral sorting effects, leading to biased estimates; for example, anomalously high La/Al2O3 ratios in European loess reflect enrichment of accessory minerals such as titanite. Employing element pairs that exhibit consistent correlations across sedimentary rock types mitigates many of these biases. The elevated abundances of heat-producing elements (K, Th, and U) in our UCC estimates suggest that the deeper continental crust, excluding the UCC, is unlikely to be dominantly felsic; instead, it is probably mafic to intermediate, depending on the assumed mantle heat flux. The new UCC composition estimate is consistent with many key geochemical ratios proposed in previous UCC estimates, such as Nb/Ta, Zr/Hf, Zr/Sm, Ni/Co, Cr/Zn, Th/U, and La/Th. Notably, the high La/Nb ratio (~2.6) supports the dominant role of arc magmatism, rather than intraplate magmatism, in crustal growth, while the Nb/Ta (12.6), (La/Yb)N (8.3), and (Dy/Yb)N (1.1) values underscore the importance of subduction-related magmatism in thick continental arcs in generating the modern continental crust.

Large-volume neutrino telescopes designed for TeV neutrino astronomy can probe the Earth’s interior through the absorption of atmospheric neutrinos traversing the planet. This provides an independent constraint on the Earth’s radial density profile, complementing conventional methods based on seismic velocity measurements. The next-generation TRopIcal DEep-sea Neutrino Telescope (TRIDENT), located in the South China Sea, is expected to offer strong sensitivity to the Earth's internal density structure. In this work, we present a study of TRIDENT’s Earth tomography sensitivity by simulating atmospheric neutrinos in the 1–100 TeV range. We reconstruct the posterior distributions of a multi-layer radial density model and investigate the impact of different geophysical constraints.We also evaluate the impact of major systematic uncertainties and study TRIDENT’s sensitivity to localized density anomalies.

Geoneutrinos are the electron antineutrinos produced by beta decays of radioactive isotopes within the Earth. By detecting them, we can obtain information about the planet's radiogenic heat production and the distribution of heat-producing elements in the Earth.

To date, four detectors (KamLAND, Borexino, SNO+, and JUNO) have successfully detected geoneutrinos.
However, these detectors are located on thick continental crust, and the high concentration of radioactive isotopes in the continental crust limits our ability to investigate deeper layers of the Earth, particularly the mantle.

To address this challenge, a project called the Ocean Bottom Detector (OBD) was proposed in 2019 by Tohoku University. The concept involves deploying a neutrino detector on the ocean floor off the coast of Hawaii, where the oceanic crust is thin and contains fewer radioactive isotopes. This location is ideal for directly observing geoneutrinos originating from the mantle.

In this presentation, we will provide an overview of the OBD project and report on the current status of prototype development.

Geophysical studies indicate that the Earth’s interior is highly heterogeneous, containing various large-scale structures. One of the most prominent features is the Large Low Velocity Provinces (LLVPs), imaged by seismic tomography as regions with anomalously slow earthquake wave velocities relative to the surrounding mantle beneath the Pacific Ocean and Africa. The origin of these structures remains debated, with one hypothesis attributing them to anomalous chemical compositions enriched in U, Th, and other heat-producing elements (HPEs).

Geoneutrinos provide a unique means of probing the distribution of these HPEs in the deep mantle. In this study, we present a feasibility study of detecting mantle heterogeneity and HPE enrichment within LLVPs using a directional geoneutrino detector. Our results demonstrate that an Ocean Bottom Detector (OBD) equipped with directional sensitivity and deployed above the Pacific LLVP could provide sensitivity to HPE enrichment within the LLVP, highlighting its potential for probing deep-mantle composition.

The Earth Potassium β⁻ decay produces antineutrinos below the 1.8 MeVinverse-beta-decay(IBD) threshold on free protons, rendering $^{40}$K geoneutrinos invisible to every detector that has observed U/Th geoneutrinos to date. Yet $^{40}$K is expected to contribute significantly to Earth’s total radiogenic heat — the largest unmeasured component of the planetary heat budget and a direct probe of the bulk silicate Earth’s volatile inventory. Measuring Potassium is recognised as critical to closing the geoneutrino-based knowledge of the Earth model.

We recently proposed a new detection methodology[1]based on charged-current antineutrino capture on $^{63}$Cu [ν̄ₑ + $^{63}$Cu → $^{63}$Ni$^{*}$ + e⁺] exploiting the event-by-event positron identification capability of aLiquidOusing a heavy-doped opaque-scintillator technology[2]to suppress backgrounds that have historically made sub-IBD-threshold antineutrino detection impractical. The positron’s unique triple-blob annihilation topology, resolved by LiquidO’s stochastic light confinement, provides the discriminating signal against solar-neutrino-induced electron backgrounds.

This talk presentsCLOUD III(first released in Venice in 2023[3]), the experimental programme designed to validate the $^{63}$Cu charged-current channel end-to-end upon the completion of the AntiMatter-OTech project programme[4]. CLOUD III aims to deploy a copper-loaded LiquidO detector at the Chooz nuclear power plant (France), approximately 35 m from a 4.25 GW$_{th}$ reactor core. The reactor’s copious antineutrino flux, which increases in the 1–2 MeV range — overlapping the $^{40}$K geoneutrino window — functions as a controlled, high-statisticstest beamfor the detection channel, enabling the first observation of $^{63}$Cu interaction and the measurement of its cross section relative to IBD on hydrogen (known to 0.2%) in the same detector volume. The talk will conclude with a discussion of the challenging scalability prospects this validated methodology offers for definitive observation of Earth’s missing potassium.

Useful References:
[1]: https://www.nature.com/articles/s42005-026-02518-6
[2]: https://www.nature.com/articles/s42005-021-00763-5
[3]: https://doi.org/10.5281/zenodo.10049845
[4]: https://doi.org/10.5281/zenodo.15198757

Determining the Earth's radiogenic heat budget depends on measuring geoneutrinos and on subtracting the lithospheric contribution reliably from the observed signal. The 500-tonne Jinping Neutrino Experiment (JNE) at the China Jinping Underground Laboratory, where the nearest nuclear power plant is about 950 km away, offers an unusually clean environment for such a measurement. We construct a near-field crustal model on a 0.2 deg x 0.2 deg grid from the SWChinaCVM-2.0 velocity structure and SWChinaCVM-MOHO-2.0 Moho depths, embed it in CRUST1.0 to define the reference model, and adopt ECM1 and CRUST1.0 alone as benchmarks. For a medium-Q bulk silicate Earth composition the reference model gives 61.5 TNU in total (+11.3/-11.6), comprising 47.4 TNU from the uranium-238 chain, 14.1 TNU from the thorium-232 chain and 52.1 TNU from the lithosphere. The near-field refinement raises the predicted signal by 1.3 TNU (about 2%) with respect to CRUST1.0 alone, whereas the ECM1 prediction lies about 6.2 TNU (about 10%) below that of CRUST1.0, so the choice of global crustal model dominates the spread among models. Reactor antineutrinos contribute 27.6 TNU, and only about one quarter of this falls inside the geoneutrino energy window. Assuming a light yield of 500 photoelectrons per MeV and an exposure of 500 t x 1500 days, some 91 geoneutrino and 41 reactor inverse beta decay events are expected. Their different spectral shapes, together with the reactor-dominated region above 3.3 MeV that fixes the reactor normalisation in situ, allow the two components and the uranium and thorium chains to be disentangled in a single spectral decomposition. These forecasts are a prerequisite for isolating the mantle signal and for confronting competing bulk silicate Earth models.

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