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

This work presents the first comprehensive joint analysis of all available Coherent Elastic Neutrino-Nucleus Scattering (CE$ν$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 $ν$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 $2 σ$ 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$ν$NS as a precision tool, reinforced by the complementarity of different experimental inputs, and lay the groundwork for future advances in the field.