Mapping reactor neutrino spectra from TAO to JUNO

TL;DR

This paper demonstrates how high-resolution measurements of reactor neutrino spectra at TAO can be accurately mapped to JUNO, enhancing the sensitivity to neutrino mass ordering despite nuclear spectrum uncertainties.

Contribution

It introduces a method to map TAO spectra to JUNO spectra accounting for energy resolution and recoil effects, improving oscillation analysis accuracy.

Findings

Mapping between TAO and JUNO spectra is highly accurate with oscillations.

Variant nuclear spectra have minimal impact on JUNO's mass ordering sensitivity.

Including TAO constraints enhances JUNO's robustness against nuclear uncertainties.

Abstract

The Jiangmen Underground Neutrino Observatory (JUNO) project aims at probing, at the same time, the two main frequencies of three-flavor neutrino oscillations, as well as their interference related to the mass ordering (normal or inverted), at a distance of ~53 km from two powerful reactor complexes in China, at Yangjiang and Taishan. In the latter complex, the unoscillated spectrum from one reactor core is planned to be closely monitored by the Taishan Antineutrino Observatory (TAO), expected to have better resolution (x 1/2) and higher statistics (x 30) than JUNO. In the context of neutrino energy spectra endowed with fine-structure features from summation calculations, we analyze in detail the effects of energy resolution and nucleon recoil on observable event spectra. We show that a model spectrum in TAO can be mapped into a corresponding spectrum in JUNO through appropriate convolutions. The mapping is exact in the hypothetical case without oscillations, and holds to a very good accuracy in the real case with oscillations. We then analyze the sensitivity to mass ordering of JUNO (and its precision oscillometry capabilities) assuming a single reference spectrum, as well as bundles of variant spectra, as obtained by changing nuclear input uncertainties in summation calculations from a publicly available toolkit. We show through a chi-squared analysis that variant spectra induce little reduction of the sensitivity in JUNO, especially when TAO constraints are included. Subtle aspects of the statistical analysis of variant spectra are also discussed.