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Register a new userThe Majorana Ge-76 Double-Beta Decay Project
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The Majorana Experiment is a next-generation Ge-76 double-beta decay search. It will employ 500 kg of Ge, isotopically enriched to 86% in Ge-76, in the form of 200 detectors in a close-packed array for high granularity. Each crystal will be electronically segmented, with each region fitted with pulse-shape analysis electronics. A half-life sensitivity is predicted of 4.2e27 y or <m_nu> < 0.02-0.07 eV, depending on the nuclear matrix elements used to interpret the data.
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The Majorana Demonstrator is a neutrinoless double-beta decay search consisting of a low-background modular array of high-purity germanium detectors, $sim2/3$ of which are enriched to 88% in $^{76}$Ge. The experiment is also searching for double-beta decay of $^{76}$Ge to excited states (e.s.) in $^{76}$Se. $^{76}$Ge can decay into three daughter states of $^{76}$Se, with clear event signatures consisting of a $betabeta$-decay followed by the prompt emission of one or two $gamma$-rays. This results with high probability in multi-detector coincidences. The granularity of the Demonstrator detector array enables powerful discrimination of this event signature from backgrounds. Using 41.9~kg-y of isotopic exposure, the Demonstrator has set world leading limits for each e.s. decay of $^{76}$Ge, with 90% CL lower half-life limits in the range of $(0.75-4.0)times10^{24}$~y. In particular, for the $2 u$ transition to the first $0^+$ e.s. of $^{76}$Se, a lower half-life limit of $7.5times10^{23}$~y at 90% CL was achieved.
GERDA, the GERmanium Detector Array experiment, is a new double beta-decay experiment which is currently under construction in the INFN National Gran Sasso Laboratory (LNGS), Italy. It is implementing a new shielding concept by operating bare Ge diodes - enriched in Ge-76 - in high purity liquid argon supplemented by a water shield. The aim of GERDA is to verify or refute the recent claim of discovery, and, in a second phase, to achieve a two orders of magnitude lower background index than recent experiments. The paper discusses motivation, physics reach, design and status of construction of GERDA, and presents some R&D results.
The MAJORANA DEMONSTRATOR is searching for double-beta decay of $^{76}$Ge to excited states (E.S.) in $^{76}$Se using a modular array of high purity Germanium detectors. $^{76}$Ge can decay into three E.S.s of $^{76}$Se. The E.S. decays have a clear event signature consisting of a $betabeta$-decay with the prompt emission of one or two $gamma$-rays, resulting in with high probability in a multi-site event. The granularity of the DEMONSTRATOR detector array enables powerful discrimination of this event signature from backgrounds. Using 21.3 kg-y of isotopic exposure, the DEMONSTRATOR has set world leading limits for each E.S. decay, with 90% CL lower half-life limits in the range of $(0.56-2.1)cdot10^{24}$ y. In particular, for the $2 u$ transition to the first $0^+$ E.S. of $^{76}$Se, a lower half-life limit of $0.68cdot10^{24}$ at 90% CL was achieved.
This paper presents a review of the search for neutrinoless double beta decay of $^{76}$Ge with emphasis on the recent results of the GERDA experiment. It includes an appraisal of fifty years of research on this topic as well as an outlook.
The observation of neutrinoless double-beta decay would determine whether the neutrino is a Majorana particle and provide information on the absolute scale of neutrino mass. The MAJORANA Collaboration is constructing the DEMONSTRATOR, an array of germanium detectors, to search for neutrinoless double-beta decay of 76-Ge. The DEMONSTRATOR will contain 40 kg of germanium; up to 30 kg will be enriched to 86% in 76-Ge. The DEMONSTRATOR will be deployed deep underground in an ultra-low-background shielded environment. Operation of the DEMONSTRATOR aims to determine whether a future tonne-scale germanium experiment can achieve a background goal of one count per tonne-year in a 4-keV region of interest around the 76-Ge neutrinoless double-beta decay Q-value of 2039 keV.
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