High sensitivity GEM experiment on 2β decay of⁷⁶Ge

Abstract

The GEM project is designed for the next generation 2β decay experiments with 76 Ge. One ton of "naked" HP Ge detectors (natural at the first GEM-I phase and enriched in 76 Ge to 86% at the second GEM-II stage) are operating in super-high purity liquid nitrogen contained in the Cu vacuum cryostat (sphere ⊘5 m). The latest is placed in the water shield ⊘11×11 m. Monte Carlo simulation evidently shows that sensitivity of the experiment (in terms of the T 1/2 limit for 0ν2β decay) is ≈10 27 yr with natural HP Ge crystals and ≈10 28 yr with enriched ones. These bounds corresponds to the restrictions on the neutrino mass m ν ≤ 0.05 eV and m ν ≤ 0.015 eV with natural and enriched detectors, respectively. Besides, the GEM-I set up could advance the current best limits on the existence of neutralinos -as dark matter candidates -by three order of magnitudes, and at the same time would be able to identify unambiguously the dark matter signal by detection of its seasonal modulation.

Neutrinoless double beta decay: Present and future

“…m ν (10 26 y) (meV) CUORE [47] 130 Te 7 27 CUORICINO [47] 130 Te 0.15 184 EXO [48] 136 Xe 8 52 GENIUS [49] 76 Ge 100 15 MAJORANA [50] 76 Ge 40 25 GEM [51] 76 Ge 70 18 MOON [52] 100 Mo 10 36 XMASS [53] 136 Xe 3 86 COBRA [54] 130 Te 0.01 240 DCBA [55] 150 Nd 0.15 190 NEMO 3 [56] 100 Mo 0.04 560 CAMEO [57] 116 Cd > 1 69 CANDLES [58] 48 Ca 1 158 [15] issue will be the capability of each project to pursue the expected background suppression. Too many proposal have been recently suggested for a detailed description.…”

“…COBRA [54] would use CdTe or CdZnTe diodes (∼10 kg) to investigate Cd and Te ββ isotopes in a calorimetric approach. GEM [51] is a proposal very similar to GENIUS in which the complex LN huge cryostat has been replaced by a definitely smaller one inserted in a large pure water container (e.g. Borexino).…”

The Gerda experiment for the search of 0νββ decay in 76Ge

“…Furthermore, the background produced by interactions of cosmic rays is lower than for the traditional concepts of HDM, IGEX or MAJORANA due to the lower Z of the shielding material. Other background sources include neutrons and gammas from the decays in the rock of the underground laboratory, radioactivity in support materials, radioactive elements in the cryogenic liquid (intrinsic, such as 39 Ar and 42 Ar, as well as externally introduced, such as radon) as well as internal backgrounds in the Ge diodes. These backgrounds were considered in the design and construction phase of GERDA and resulted in specific design choices, selection of materials used and also in how detectors were handled.…”

“…A similar experimental setup has been proposed previously in Ref. [39]. The detectors are lowered into the LAr volume using a lock system located in a clean room on top of the water tank.…”

“…Notice, that the spectrum from the natural detectors has been renormalized to match the exposure of the enriched diodes. The low energy part is dominated by the β decay of 39 Ar which has an endpoint energy of 565 keV. The well known activity of A( 39 Ar) = [1.01 ± 0.02(stat) ± 0.08(syst)] Bq/kg (Ref.…”