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Register a new userA Low Energy Rare Event Search with the Majorana Demonstrator
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The MAJORANA DEMONSTRATOR is sensitive to rare events near its energy threshold, including bosonic dark matter, solar axions, and lightly ionizing particles. In this analysis, a novel training set of low energy small-angle Compton scatter events is used to determine the efficiency of pulse shape analysis cuts, and we present updated bosonic dark matter and solar axion results from an 11.17 kg-y dataset using a 5 keV analysis threshold.
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A brief review of the history and neutrino physics of double beta decay is given. A description of the MAJORANA DEMONSTRATOR research and development program including background reduction techniques is presented in some detail. The application of point contact (PC) detectors to the experiment is discussed, including the effectiveness of pulse shape analysis. The predicted sensitivity of a PC detector array enriched to 86% in 76Ge is given.
Neutrinoless double-beta decay is a hypothesized process where in some even-even nuclei it might be possible for two neutrons to simultaneously decay into two protons and two electrons without emitting neutrinos. This is possible only if neutrinos are Majorana particles, i.e. fermions that are their own antiparticles. Neutrinos being Majorana particles would explicitly violate lepton number conservation, and might play a role in the matter-antimatter asymmetry in the universe. The observation of neutrinoless double-beta decay would also provide complementary information related to neutrino masses. The Majorana Collaboration is constructing the Majorana Demonstrator, a 40-kg modular germanium detector array, to search for the Neutrinoless double-beta decay of 76Ge and to demonstrate a background rate at or below 3 counts/(ROI-t-y) in the 4 keV region of interest (ROI) around the 2039 keV Q-value for 76Ge Neutrinoless double-beta decay. In this paper, we discuss the physics of neutrinoless double beta decay and then focus on the Majorana Demonstrator, including its design and approach to achieve ultra-low backgrounds and the status of the experiment.
The MJ Collaboration is operating an array of high purity Ge detectors to search for neutrinoless double-beta decay in $^{76}$Ge. The MJ DEM comprises 44.1~kg of Ge detectors (29.7 kg enriched in $^{76}$Ge) split between two modules contained in a low background shield at the Sanford Underground Research Facility in Lead, South Dakota. Here we present results from data taken during construction, commissioning, and the start of full operations. We achieve unprecedented energy resolution of 2.5 keV FWHM at qval and a very low background with no observed candidate events in 10 kg yr of enriched Ge exposure, resulting in a lower limit on the half-life of $1.9times10^{25}$ yr (90% CL). This result constrains the effective Majorana neutrino mass to below 240 to 520 meV, depending on the matrix elements used. In our experimental configuration with the lowest background, the background is $4.0_{-2.5}^{+3.1}$ counts/(FWHM t yr).
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.
Neutrinoless double-beta decay searches seek to determine the nature of neutrinos, the existence of a lepton violating process, and the effective Majorana neutrino mass. The {sc Majorana} Collaboration is assembling an array of high purity Ge detectors to search for neutrinoless double-beta decay in $^{76}$Ge. The {sc Majorana Demonstrator} is composed of 44.8~kg (29.7 kg enriched in $^{76}$Ge) of Ge detectors in total, split between two modules contained in a low background shield at the Sanford Underground Research Facility in Lead, South Dakota. The initial goals of the {sc Demonstrator} are to establish the required background and scalability of a Ge-based, next-generation, tonne-scale experiment. Following a commissioning run that began in 2015, the first detector module started physics data production in early 2016. We will discuss initial results of the Module 1 commissioning and first physics run, as well as the status and potential physics reach of the full {sc Majorana Demonstrator} experiment. The collaboration plans to complete the assembly of the second detector module by mid-2016 to begin full data production with the entire array.
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