Search for double beta decay of Mo with liquid argon ionization chamber (first results)

First two runs with 138.7 g of ¹⁰⁰Mo were done 9202 h and 238 h). Limits on half-lives for 0ν- and 0νχ⁰-decays of ¹⁰⁰Mo were obtained, > 2.3 · 10²¹ y and 0.8 · 10²⁰ y, respectively at 90% CL. Also the limit on the content of radioactive ⁴²Ar in the natural Ar was obtained, < 5 · 10⁻²¹ g/g. Perspectives for the future are discussed.     

Double beta decay of 100Mo

Two-neutrino double beta decay of ¹⁰⁰Mo with half-life T _1/2=[7.2±0.9(stat)± 1.8(syst)]×10¹⁸ yr was detected using a liquid argon ionization chamber. With a C.L. of 68% (90%), the bounds on neutrinoless decay and decay with majoron emission were found to be 8.4(4.9)×10²¹ and 4.1(3.2)×10²⁰ yr, respectively. An analysis of all available results provides the average “world” value T _1/2=(8.0±0.7)×10¹⁸ yr for the two-neutrino decay of ¹⁰⁰Mo, and the corresponding nuclear matrix element is M _GT=0.118±0.005.