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1. Assay-based background projection for the Majorana Demonstrator using Monte Carlo uncertainty propagation

   https://doi.org/10.1103/PhysRevC.110.055804  

   Arnquist, I J; Avignone, F T; Barabash, A S; Barton, C J; Bhimani, K H; Blalock, E; Bos, B; Busch, M; Caldwell, T S; Chan, Y-D; et al (November 2024, Physical Review C)

   The background index (BI) is an important quantity to project and calculate the half-life sensitivity of neutrinoless double-𝛽 decay (0⁢𝜈⁢𝛽⁢𝛽) experiments. An analysis framework is presented to calculate the BI using the specific activities, masses, and simulated efficiencies of an experiments components as distributions. This Bayesian framework includes a unified approach to combine specific activities from assay. Monte Carlo uncertainty propagation is used to build a BI distribution from the specific activity, mass, and efficiency distributions. This method is applied to the Majorana Demonstrator, which deployed arrays of high-purity Ge detectors enriched in 76Ge to search for 0⁢𝜈⁢𝛽⁢𝛽. The original assay-based projection is requantified in the new framework, using the as-built geometry of the Demonstrator and additional assay information. While 47% higher than the original projection, the resulting BI of [8.95±0.36]×10−4cts/(keVkgyr) from the 232Th and 238U decay chains does not account for the higher-than-expected BI observed by the Demonstrator. This method enables us to demonstrate the statistical incompatibility between the Demonstrator's observed background and the assay results. 

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2. The Majorana Demonstrator readout electronics system

   https://doi.org/10.1088/1748-0221/17/05/T05003  

   Abgrall, N.; Amman, M.; Arnquist, I.J.; Avignone, F.T.; Barabash, A.S.; Barton, C.J.; Barton, P.J.; Bertrand, F.E.; Bhimani, K.H.; Bos, B.; et al (May 2022, Journal of Instrumentation)

   Abstract The Majorana Demonstrator comprises two arrays of high-purity germanium detectors constructed to search for neutrinoless double-beta decay in 76 Ge and other physics beyond the Standard Model. Its readout electronics were designed to have low electronic noise, and radioactive backgrounds were minimized by using low-mass components and low-radioactivity materials near the detectors. This paper provides a description of all components of the Majorana Demonstrator readout electronics, spanning the front-end electronics and internal cabling, back-end electronics, digitizer, and power supplies, along with the grounding scheme. The spectroscopic performance achieved with these readout electronics is also demonstrated. 

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3. First Results on the Search for Lepton Number Violating Neutrinoless Double-β Decay with the LEGEND-200 Experiment

   https://doi.org/10.1103/25tk-nctn  

   Acharya, H; Ackermann, N; Agostini, M; Alexander, A; Andreoiu, C; Araujo, G R; Avignone, F T; Babicz, M; Bae, W; Bakalyarov, A M; et al (January 2026, Physical Review Letters)

   The LEGEND Collaboration is searching for neutrinoless double-beta ( $0\nu \beta \beta$ ) decay by operating high-purity germanium detectors enriched in ${}^{76}\mathrm{Ge}$ in a low-background liquid argon environment. Building on key technological innovations from the GERmanium Detector Array (GERDA) experiment and the MAJORANA DEMONSTRATOR experiment, LEGEND-200 has performed a first $0\nu \beta \beta$ decay search based on 61.0 kg yr of data. Over half of this exposure comes from our highest performing detectors, including newly developed inverted-coaxial detectors, and is characterized by an estimated background level of ${0.5}_{-0.2}^{+0.3}\mathrm{cts}/\left(\mathrm{keV}\mathrm{ton}\mathrm{yr}\right)$ in the $0\nu \beta \beta$ decay signal region. A combined analysis of data from GERDA, the MAJORANA DEMONSTRATOR, and LEGEND-200, characterized by a 90% confidence level exclusion sensitivity of $2.8\times {10}^{26}\mathrm{yr}$ on the half-life of $0\nu \beta \beta$ decay, reveals no evidence for a signal and sets a new observed lower limit at $T_{1/2}^{0\nu }>1.9\times {10}^{26}\mathrm{yr}$ (90% confidence level). Assuming the decay is mediated by Majorana neutrinos, this corresponds to an upper limit on the effective Majorana mass in the range $m_{\beta \beta }<75–200\mathrm{meV}$ , depending on the adopted nuclear matrix element. 

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4. Supplemental Material for "First Results on the Search for Lepton Number Violating Neutrinoless Double Beta Decay with the LEGEND-200 Experiment"

   https://doi.org/10.5281/zenodo.15411218  

   LEGEND_Collaboration (January 2025, Zenodo)

   Abstract: [l200-event-list.csv] Table of events detected by LEGEND-200 in the [1930, 2160] keV HPGe energy range surviving all cuts. The two events at 2118.46 keV and at 2118.78 keV are excluded in the following analysis, being associated to the gamma line of 214Bi. [l200-partition-parameters.csv] Table of LEGEND-200 experimental parameters for each HPGe detector and each time period characterized by stable performance. The combined 0vbb acceptance incorporates all other acceptances and enrichment fractions, with uncertainties added in quadrature. energy_bias_in_keV is defined as the Q-value of double-beta decay (2039.06 keV) minus calibrated energy. See the main body of the letter for more details about the definition of these parameters and how they are used in the likelihood function for the 0vbb analysis. event-list and partition-parameters files for the GERDA and MAJORANA DEMONSTRATOR datasets can be downloaded at (respectively): 10.5281/zenodo.15031465 10.1103/PhysRevLett.130.062501 (Supplemental Material) [l200-0vbb-rate-posterior.csv] [ge76-comb-0vbb-rate-posterior.csv] Normalized histogram of the (Bayesian) posterior distribution for the 0vbb signal half-rate parameter Γ_1/2, calculated using a uniform prior distribution. l200-0vbb-rate-posterior.csv refers to the LEGEND-200 data set, while ge76-comb-0vbb-rate-posterior.csv refers to the combined analysis of GERDA, MAJORANA DEMONSTRATOR and LEGEND data. [profile-likelihood.csv] Likelihood for the analysis of the LEGEND-200 data set and the combined data set, as a function of the 0vbb signal half-rate parameter Γ_1/2 and profiled over all other parameters. 

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5. Energy calibration of germanium detectors for the Majorana Demonstrator

   https://doi.org/10.1088/1748-0221/18/09/P09023  

   Arnquist, IJ; Avignone_III, FT; Barabash, AS; Barton, CJ; Bhimani, KH; Blalock, E; Bos, B; Busch, M; Buuck, M; Caldwell, TS; et al (September 2023, Journal of Instrumentation)

   Abstract TheMajorana Demonstratorwas a search for neutrinoless double-beta decay (0νββ) in the⁷⁶Ge isotope. It was staged at the 4850-foot level of the Sanford Underground Research Facility (SURF) in Lead, SD. The experiment consisted of 58 germanium detectors housed in a low background shield and was calibrated once per week by deploying a²²⁸Th line source for 1 to 2 hours. The energy scale calibration determination for the detector array was automated using custom analysis tools. We describe the offline procedure for calibration of theDemonstratorgermanium detectors, including the simultaneous fitting of multiple spectral peaks, estimation of energy scale uncertainties, and the automation of the calibration procedure. 

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