Breakthrough into the Sub-eV Neutrino Mass Range: Status of the HEIDELBERG-MOSCOW Double Beta Decay Experiment with enriched $^{76}$Ge

TL;DR

The Heidelberg-Moscow experiment set a new sub-eV neutrino mass limit through non-observation of neutrinoless double beta decay, also providing high-statistics data on two-neutrino decay and dark matter constraints.

Contribution

First experiment to probe the sub-eV neutrino mass range via neutrinoless double beta decay with high statistical significance.

Findings

No signal for neutrinoless decay, half-life > 5.1×10^{24} years.

Measured two-neutrino decay half-life as (1.53±0.04±0.13)×10^{24} years.

Established the strictest limits on WIMP dark matter detection.

Abstract

Recent results of the Heidelberg-Moscow double beta decay experiment are presented. After 8.6 kg$\cdot$a of measuring time no signal is seen for the neutrinoless decay mode. A half-life limit of $T_{1/2}^{0\nu\beta\beta} > 5.1\cdot 10^{24}$~a is deduced which converts into a neutrino mass limit of $\langle m_{\nu_e}\rangle < 0.68 $ eV (90\% CL). The experiment thus is the first one penetrating into the sub-eV range for the neutrino mass. For the $2\nu$ mode a half life of $T_{1/2}^{2\nu\beta\beta} = (1.53\pm0.04 _{stat}\pm0.13_{sys})\cdot 10^{24}$ a is derived. More than 10000 $2\nu$ double beta events are observed. This is the first high statistics observation of this nuclear decay mode. Limits on more exotic decay modes are also presented. Concerning dark matter the experiment now gives the sharpest limits for the observation of WIMPs.