K. Gusev

The MAJORANA DEMONSTRATOR Neutrinoless Double-Beta Decay Experiment

The MAJORANA DEMONSTRATOR will search for the neutrinoless double-beta decay of the isotope Ge with a mixed array of enriched and natural germanium detectors. The observation of this rare decay would indicate that the neutrino is its own antiparticle, demonstrate that lepton number is not conserved, and provide information on the absolute mass scale of the neutrino. The DEMONSTRATOR is being assembled at the 4850-foot level of the Sanford Underground Research Facility in Lead, South Dakota. The array will be situated in a low-background environment and surrounded by passive and active shielding. Here we describe the science goals of the DEMONSTRATOR and the details of its design.

The Majorana Parts Tracking Database

The Majorana Demonstrator is an ultra-low background physics experiment searching for the neutrinoless double beta decay of 76 Ge. The Majorana Parts Tracking Database is used to record the history of components used in the construction of the Demonstrator. The tracking implementation takes a novel approach based on the schema-free database technology CouchDB. Transportation, storage, and processes undergone by parts such as machining or cleaning are linked to part records. Tracking parts provides a great logistics benefit and an important quality a ssurance reference during construction. In addition, the l ocation history of parts provides an estimate of their exposure to cosmic radiation. A web application for data entry and a radiation exposure calculator have been developed as tools for achieving the extreme radio-purity required for this rare decay search.

Status of the MAJORANA DEMONSTRATOR experiment

The Majorana Demonstrator neutrinoless double beta-decay experiment is currently under construction at the Sanford Underground Research Facility in South Dakota, USA. An overview and status of the experiment are given.

Investigation of the 2νEC/EC Decay of 106Cd

Search for the β+β+, β+EC, and EC/EC modes of the 106Cd decay was carried out with the TGV-2 (Telescope Germanium Vertical) low-background multidetector spectrometer installed at the Modane underground laboratory (4800 m w.e.). The measured foil samples ∼50 μm thick and 52 mm in diameter were placed between the entrance windows of the neighboring detectors inside the cryostat. The total measurement time for 10 g of 106Cd enriched to 75% was 8687 h. New limits (at the 90% confidence level, CL) were obtained for the 106Cd half-lives against various branches of the decay to the ground state 0+ and excited states 2+ of the 106Pd daughter nucleus. They are T1/2(2νβ+β+) ≥ 6.0 × 1019 y, and T1/2(2νβ+EC) ≥ 5.9 × 1019 y, and T1/2(2νEC/EC) ≥ 3.0 × 1020 y for the transitions to the 0+ ground state of 106Pd; T1/2(2νβ+β+) ≥ 5.7 × 1019 y, T1/2(2νβ+EC) ≥ 5.9 × 1019 y, and T1/2(2νEC/EC) ≥ 4.2 × 1019 y for the transitions to the 2+, 512-keV excited state of 106Pd; and T1/2(2νEC/EC) ≥ 3.1 × 1019 y for the transition to the 01+, 1334-keV excited state of 106Pd.

The TGV II Experiment (Phase I Results)

The TGV II (Telescope Germanium Vertical) facility is a low background spectrometer operated in Modane Underground Laboratory. It aims at the study of double electron capture of 106Cd. The spectrometer is composed of 32 HPGe planar detectors interleaved with thin‐foil samples made of Cd‐106 enriched to 75% (total mass about 10 g). In 2006, the main run of phase I (1 year duration) was terminated yielding a new limit on half‐life for two‐neutrino double electron capture (g.s.→g.s.) in 106Cd as 2.0×1020u2009years. This limit is significantly higher (by almost three orders of magnitude) than those already published.