Liquid Argon Ionization Detector for Double Beta Decay Studies

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.

15 pages, 11 figures, 10 authors