# Ge Detectors and $0\nu\beta\beta$: The Search for Double Beta Decay with Germanium Detectors: Past, Present and Future

## TL;DR

Germanium detectors, with their excellent energy resolution and low background, have been instrumental in the search for neutrinoless double beta decay, with recent experiments approaching half-life sensitivities beyond 10^26 years and plans to reach 10^28 years.

## Contribution

This paper reviews the historical development, current status, and future prospects of Germanium detectors in neutrinoless double beta decay searches, highlighting technological advancements and collaborative efforts.

## Key findings

- GERDA and Majorana have achieved background levels near 10^26 years.
- Innovations in detector shielding and material purity have significantly improved sensitivity.
- The upcoming LEGEND experiment aims to extend the half-life limit beyond 10^28 years.

## Abstract

High Purity Germanium Detectors have excellent energy resolution; the best among the technologies used in double beta decay. Since neutrino-less double beta decay hinges on the search for a rare peak upon a background continuum, this strength has enabled the technology to consistently provide leading results. The Ge crystals at the heart of these experiments are very pure; they have no measurable U or Th contamination. The added efforts to reduce the background associated with electronics, cryogenic cooling, and shielding have been very successful, leading to the longevity of productivity. The first experiment published in 1967 by the Milan group of Fiorini, established the benchmark half-life limit $>3\times10^{20}$ yr. More recently, the \MJ\ and GERDA collaborations have developed new detector technologies that optimize the pulse waveform analysis. As a result, the GERDA collaboration refuted the claim of observation with a revolutionary approach to shielding by immersing the detectors directly in radio-pure liquid argon. In 2018, the \MJ\ collaboration, using a classic vacuum cryostat and high-Z shielding, achieved a background level near that of GERDA by developing very pure materials for use nearby the detectors. Together, GERDA and \MJ\ have provided limits approaching $10^{26}$ yr. In this article, we elaborate on the historical use of Ge detectors for double beta decay addressing the strengths and weaknesses. We also summarize the status and future as many \MJ\ and GERDA collaborators have joined with scientists from other efforts to give birth to the LEGEND collaboration. LEGEND will exploit the best features of both experiments to extend the half-life limit beyond $10^{28}$ yr with a ton-scale experiment.