Search for Sterile Neutrinos with CUPID-0

TL;DR

This study used the CUPID-0 experiment to search for sterile neutrinos via spectral distortions in double beta decay, setting new upper limits on their mixing with active neutrinos in the 0.5-1.5 MeV mass range.

Contribution

First to utilize CUPID-0 data for sterile neutrino search through spectral analysis of double beta decay with detailed background modeling.

Findings

No evidence of sterile neutrinos was found.

Established the most stringent upper limit on active-sterile mixing at 0.7 MeV.

Set constraints on sterile neutrino properties in the 0.5-1.5 MeV mass range.

Abstract

Sterile neutrinos are well-motivated extensions of the Standard Model, introduced to address fundamental questions such as the origin of neutrino masses and the nature of dark matter. Exploiting the precise data reconstruction achieved by the CUPID-0 experiment, we searched for spectral distortions in the double $\beta$-decay of $^{82}$Se compatible with the emission of a sterile neutrino. The analysis relies on the construction of a detailed background model down to 200 keV, enabling an accurate characterization of the main sources of contamination. Using a Zn$^{82}$Se exposure of 9.95 kg$\cdot$yr, we explored sterile neutrino mass hypotheses between 0.5 MeV and 1.5 MeV. No evidence for a signal was observed in any scenario; therefore, we derived 90% C.I. upper limits on the active-sterile mixing probability $\sin^2\theta$, obtaining the most stringent bound, $\sin^2\theta<8\times 10^{-3}$, for a sterile neutrino mass of 0.7 MeV.