Liquid Argon Ionization Detector for Double Beta Decay Studies

TL;DR

This paper reports on the development and deployment of a liquid argon ionization detector for double beta decay studies, measuring the decay of $^{100}$Mo and setting limits on neutrinoless modes, with additional findings on argon purity.

Contribution

The paper introduces a new multisection liquid argon detector specifically designed for double beta decay research, providing experimental measurements and limits.

Findings

Observed $eta eta (2 u)$ decay of $^{100}$Mo with a half-life of about 7.2 x 10^{18} years.

Set lower limits on neutrinoless double beta decay modes: >8.4 x 10^{21} years at 68% C.L.

Determined upper limits on $^{42}$Ar content and $^{222}$Rn activity in liquid argon.

Abstract

A multisection liquid argon ionization detector was developed by the DBA collaboration to study the double beta- decay of $^{100}$Mo. The experiment was carried out in the Gran Sasso underground laboratory in Italy. The detector design and main characteristics are described. The $\beta \beta (2\nu)$ decay of $^{100}$Mo was observed and its half-life measured: $T_{1/2}=[7.2 \pm 0.9(stat) \pm 1.8(syst)] \times 10^{18}$ yr. Limits on the 0$\nu $ and 0$\nu \chi ^{0}$ modes of the decay were obtained: $T_{1/2}> 8.4(4.9) \times 10^{21}$ yr and $T_{1/2}> 4.1(3.2)\times 10^{20}$ yr at 68% (90%) C.L., respectively. In addition the upper limits on the $^{42}$Ar content and $^{222}$Rn activity in liquid Ar were found to be $4.3 \times 10^{-21}$ g/g and $1.2 \times 10^{-3}$ Bq/kg, respectively.