Worldwide Reactor Neutrino Propagation to Underground Labs: Matter Effects and Flux Predictions

TL;DR

This paper develops a high-precision framework for predicting reactor neutrino fluxes at underground labs, accounting for matter effects in the Earth to improve geoneutrino research accuracy.

Contribution

It introduces a novel computational approach using a second-order Strang-splitting solver to incorporate Earth's matter effects into reactor neutrino flux predictions.

Findings

Quantified the impact of Earth's matter effects on reactor neutrino oscillations.

Compared 1D and 3D Earth models to evaluate structural influence on flux predictions.

Enhanced the accuracy of reactor neutrino flux models for geophysical applications.

Abstract

As a unique probe for geophysical research, geoneutrinos can reveal the distribution of internal heat sources in the Earth by detecting electron antineutrinos produced by the radioactive decay of $^{238}$U, $^{232}$Th, and $^{40}$K. However, commercial nuclear power plants continuously produce the same type of electron antineutrinos, which constitute a primary background difficult to eliminate in geoneutrino experiments. As geoneutrino measurements and reactor background modeling approach sub-percent precision, even small matter-induced corrections to reactor antineutrino propagation require quantitative assessment. In this paper, we develop a high-precision prediction framework for reactor neutrino fluxes at underground labs, using global reactor operating data, reactor-to-detector distances, and matter effects (MSW) on neutrino propagation through the Earth. To solve the three-flavor MSW evolution efficiently, we implement a second-order Strang-splitting solver in the vacuum mass basis. Within this framework, we have calculated the reactor neutrino oscillation probabilities, including the MSW effect under one-dimensional (spherically symmetric) and three-dimensional (including lateral inhomogeneities) Earth models, and compared them with the vacuum oscillation scenario, to assess the impact of Earth's structural features on the accuracy of reactor neutrino flux predictions.