Improved limit on neutrinoless double beta decay of $^{76}$Ge from GERDA Phase II

TL;DR

The GERDA Phase II experiment set a new lower limit on the neutrinoless double beta decay half-life of $^{76}$Ge, achieving the lowest background level and improving sensitivity over previous results.

Contribution

This work provides the most stringent limit to date on neutrinoless double beta decay of $^{76}$Ge, utilizing enhanced detector exposure and advanced background suppression techniques.

Findings

Background level of $1.0_{-0.4}^{+0.6} imes 10^{-3}$ cts/(keV·kg·yr) achieved

No decay signal observed within the sensitivity range

Lower limit on decay half-life set at $8.0 imes 10^{25}$ years

Abstract

The GERDA experiment searches for the lepton number violating neutrinoless double beta decay of $^{76}$Ge ($^{76}$Ge $\rightarrow$ $^{76}$Se + 2e$^-$) operating bare Ge diodes with an enriched $^{76}$Ge fraction in liquid argon. The exposure for BEGe-type detectors is increased threefold with respect to our previous data release. The BEGe detectors feature an excellent background suppression from the analysis of the time profile of the detector signals. In the analysis window a background level of $1.0_{-0.4}^{+0.6}\cdot10^{-3}$ cts/(keV$\cdot$kg$\cdot$yr) has been achieved; if normalized to the energy resolution this is the lowest ever achieved in any 0$\nu\beta\beta$ experiment. No signal is observed and a new 90 \% C.L. lower limit for the half-life of $8.0\cdot10^{25}$ yr is placed when combining with our previous data. The median expected sensitivity assuming no signal is $5.8\cdot10^{25}$ yr.