Abstract
The MajoranaDemonstratorwill search for the neutrinoless double-beta(ββ0ν)decay of the isotopeGe 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 Demonstratoris 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 Demonstratorand the details of its design.
Highlights
We describe the Majorana Demonstrator as an experimental effort under construction in the Sanford Underground Research Facility (SURF) whose goal is to demonstrate the techniques required for a definitive next-generation ββ(0])-decay experiment with enriched Ge detectors
A method for building this library from a large number of measured signals has been developed and tested with simulation and experimental studies. Results of this optimized pulse-shape analysis (PSA) algorithm on P-PC data are shown in Figure 3, where the high spectrum is for all events from a 232Th source, and the low spectrum is for events that pass the PSA cut
The 42.5 kg of 86% enriched 76Ge has been reduced from GeO2 and refined to electronic grade Ge with a yield of 98%
Summary
Neutrinoless double-beta (ββ(0])) decay searches represent the only viable experimental method for testing the Majorana nature of neutrinos [9] The observation of this process would immediately imply that lepton number is violated and that neutrinos are Majorana particles [10]. Evidence from the SNO experiment [2] of a clear departure from nonmaximal mixing in solar neutrino oscillation implies a minimum effective Majorana neutrino mass of ∼15 meV for the inverted hierarchy scenario This target is within reach of next-generation ββ(0]) searches. The Majorana Demonstrator can search for solar axions generated by the bremsstrahlung mechanism in the sun [46] and detected by the axioelectric effect [47] Since this axion spectrum peaks at about 0.6 keV and falls sharply by an order of magnitude by about 3 keV, the low threshold and background are keys for this measurement. Such an effort could demonstrate the feasibility of P-PC technology for reactor monitoring and nuclear treaty verification
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