Joint analysis of reactor and accelerator CE$\nu$NS data on germanium: implications for the Standard Model and nuclear physics

TL;DR

This paper performs a comprehensive joint analysis of all available germanium CEνNS data from reactors and spallation sources, refining Standard Model parameters and exploring tensions with theoretical predictions to advance nuclear physics and neutrino research.

Contribution

It is the first to combine all germanium CEνNS data from multiple experiments, providing improved parameter estimates and analyzing systematic uncertainties affecting the Standard Model.

Findings

Determined germanium neutron rms radius with high precision.

Identified a 2σ tension between COHERENT data and Standard Model predictions.

Highlighted the importance of nuclear form factors and flux normalization in CEνNS analysis.

Abstract

This work presents the first comprehensive joint analysis of all available Coherent Elastic Neutrino-Nucleus Scattering (CE$\nu$NS) data on germanium: those observed at the Spallation Neutron Source (SNS) by the COHERENT collaboration and those of the nuclear reactors revealed by the CONUS+ experiment using germanium detectors. In addition to COHERENT and CONUS+, we incorporate reactor data from TEXONO and $\nu$GeN, thereby enhancing both the statistical significance and the systematic reliability of our study. We provide state-of-the-art determinations of key nuclear physics and Standard Model parameters, including the neutron root-mean-square (rms) radius of germanium nuclei, the weak mixing angle, and the neutrino charge radius. The observed tension of about $2 \sigma$ between the COHERENT germanium measurement and the Standard Model prediction motivates a detailed reassessment of the theoretical cross-section. In particular, we examine the impact of nuclear form factors and uncertainties in the nuclear radius, as well as the potential influence of a systematic shift in the neutrino flux normalisation at the SNS. Our results highlight the reliability of CE$\nu$NS as a precision tool, reinforced by the complementarity of different experimental inputs, and lay the groundwork for future advances in the field.