Evidence of Single State Dominance in the Two-Neutrino Double-$\beta$ Decay of Se-82 with CUPID-0

TL;DR

This study measures the two-neutrino double-beta decay of Se-82 using cryogenic calorimeters, achieving high precision in half-life determination and providing evidence that the decay is dominated by a single state, challenging higher state dominance models.

Contribution

First measurement of Se-82 two-neutrino double-beta decay with cryogenic calorimeters, confirming single state dominance with high statistical significance.

Findings

Precise half-life measurement: (8.60 ± 0.03 (stat.) +0.17/-0.10 (syst.)) × 10^{19} yr

High signal-to-background ratio enabled background source reconstruction

Single state dominance is favored over higher state dominance at 5.5 sigma

Abstract

We report on the measurement of the two-neutrino double-$\beta$ decay of $^{82}$Se performed for the first time with cryogenic calorimeters, in the framework of the CUPID-0~experiment. With an exposure of 9.95 kg$\times$yr of Zn$^{82}$Se, we determine the two-neutrino double-$\beta$ decay half-life of $^{82}$Se with an unprecedented precision level, $T_{1/2}^{2\nu} = [8.60 \pm 0.03 \textrm{(stat.)}~^{+0.17}_{-0.10} \textrm{(syst.)}] \times 10^{19}~\textrm{yr}$. The very high signal-to-background ratio, along with the detailed reconstruction of the background sources allowed us to identify the single state dominance as the underlying mechanism of such process, demonstrating that the higher state dominance hypothesis is disfavored at the level of 5.5 $\sigma$.