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Charge conservation and the Pauli exclusion principle result from fundamental symmetries in the standard model of particle physics, and are typically taken as axiomatic. High-precision tests for small violations of these symmetries could point to new physics. Here we consider three models for violation of these processes, which would produce detectable ionization in the high-purity germanium detectors of the M ajorana D emonstrator experiment. Using a 37.5 kg yr exposure, we report a lower limit on the electron mean lifetime, improving the previous best limit for the e → ν e ν e ¯ ν e decay channel by more than an order of magnitude. We also present searches for two types of violation of the Pauli exclusion principle, setting limits on the probability of an electron to be found in a symmetric quantum state. The M ajorana D emonstrator experiment reports searches for the violation of the Pauli exclusion principle and of charge conservation. In the absence of a signal, exclusion limits for these processes are reported.

The Majorana Demonstrator was an ultra-low-background experiment designed for neutrinoless double-beta decay (\\(0\\nu\\beta\\beta\\)) investigation in \\(^{76}\\)Ge. Located at the Sanford Underground Research Facility in Lead, South Dakota, the Demonstrator utilized modular high-purity Ge detector arrays within shielded vacuum cryostats, operating deep underground. The arrays, with a capacity of up to 40.4 kg (27.2 kg enriched to \\(\\sim 88\\%\\) in \\(^{76}\\)Ge), have accumulated the full data set, totaling 64.5 kg yr of enriched active exposure and 27.4 kg yr of exposure for natural detectors. Our updated search improves previously explored three-nucleon decay modes in Ge isotopes, setting new partial lifetime limits of \\(1.83\\times10^{26}\\) years (90\\% confidence level) for \\(^{76}\\)Ge(\\(ppp\\)) \\(\\rightarrow\\) \\(^{73}\\)Cu e\\(^+\\pi^+\\pi^+\\) and \\(^{76}\\)Ge(\\(ppn\\)) \\(\\rightarrow\\) \\(^{73}\\)Zn e\\(^+\\pi^+\\). The partial lifetime limit for the fully inclusive tri-proton decay mode of \\(^{76}\\)Ge is found to be \\(2.1\\times10^{25}\\) yr. Furthermore, we have updated limits for corresponding multi-nucleon decays.

The Majorana Demonstrator is a leading experiment searching for neutrinoless double-beta decay with high purity germanium detectors (HPGe). Machine learning provides a new way to maximize the amount of information provided by these detectors, but the data-driven nature makes it less interpretable compared to traditional analysis. An interpretability study reveals the machine's decision-making logic, allowing us to learn from the machine to feedback to the traditional analysis. In this work, we have presented the first machine learning analysis of the data from the Majorana Demonstrator; this is also the first interpretable machine learning analysis of any germanium detector experiment. Two gradient boosted decision tree models are trained to learn from the data, and a game-theory-based model interpretability study is conducted to understand the origin of the classification power. By learning from data, this analysis recognizes the correlations among reconstruction parameters to further enhance the background rejection performance. By learning from the machine, this analysis reveals the importance of new background categories to reciprocally benefit the standard Majorana analysis. This model is highly compatible with next-generation germanium detector experiments like LEGEND since it can be simultaneously trained on a large number of detectors.

With excellent energy resolution and ultra-low level radiogenic backgrounds, the high-purity germanium detectors in the Majorana Demonstrator enable searches for several classes of exotic dark matter (DM) models. In this work, we report new experimental limits on keV-scale sterile neutrino DM via the transition magnetic moment from conversion to active neutrinos, \\(_s _a\\). We report new limits on fermionic dark matter absorption (\\( + A + A\\)) and sub-GeV DM-nucleus 3\\(\\)2 scattering (\\( + + A + A\\)), and new exclusion limits for bosonic dark matter (axionlike particles and dark photons). These searches utilize the (1--100)-keV low energy region of a 37.5-kg y exposure collected by the Demonstrator between May 2016 and November 2019, using a set of \\(^76\\)Ge-enriched detectors whose surface exposure time was carefully controlled, resulting in extremely low levels of cosmogenic activation.

The background index is an important quantity which is used in projecting and calculating the half-life sensitivity of neutrinoless double-beta decay (\\(0\\nu\\beta\\beta\\)) experiments. A novel analysis framework is presented to calculate the background index using the specific activities, masses and simulated efficiencies of an experiment's 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 background index distribution from the specific activity, mass and efficiency distributions. This analysis method is applied to the MAJORANA DEMONSTRATOR, which deployed arrays of high-purity Ge detectors enriched in \\(^{76}\\)Ge to search for \\(0\\nu\\beta\\beta\\). The framework projects a mean background index of \\(\\left[8.95 \\pm 0.36\\right] \\times 10^{-4}\\)cts/(keV kg yr) from \\(^{232}\\)Th and \\(^{238}\\)U in the DEMONSTRATOR's components.

The MAJORANA DEMONSTRATOR was a search for neutrinoless double-beta decay (\\(0\\nu\\beta\\beta\\)) in the \\(^{76}\\)Ge 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 a \\(^{228}\\)Th 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 the Demonstrator germanium detectors, including the simultaneous fitting of multiple spectral peaks, estimation of energy scale uncertainties, and the automation of the calibration procedure.

Axions were originally proposed to explain the strong-CP problem in QCD. Through the axion-photon coupling, the Sun could be a major source of axions, which could be measured in solid state detection experiments with enhancements due to coherent Primakoff-Bragg scattering. The Majorana Demonstrator experiment has searched for solar axions with a set of \\(^{76}\\)Ge-enriched high purity germanium detectors using a 33 kg-yr exposure collected between Jan. 2017 and Nov. 2019. A temporal-energy analysis gives a new limit on the axion-photon coupling as \\(g_{a\\gamma}<1.45\\times 10^{-9}\\) GeV\\(^{-1}\\) (95% C.I.) for axions with mass up to 100 eV/\\(c^2\\). This improves laboratory-based limits between about 1 eV/\\(c^2\\) and 100 eV/\\(c^2\\).

The Precision Reactor Oscillation and Spectrum Experiment, PROSPECT, has made world-leading measurements of reactor antineutrinos at short baselines. In its first phase, conducted at the High Flux Isotope Reactor (HFIR) at Oak Ridge National Laboratory, PROSPECT produced some of the strongest limits on eV-scale sterile neutrinos, made a precision measurement of the reactor antineutrino spectrum from \\(^{235}\\)U, and demonstrated the observation of reactor antineutrinos in an aboveground detector with good energy resolution and well-controlled backgrounds. The PROSPECT collaboration is now preparing an upgraded detector, PROSPECT-II, to probe yet unexplored parameter space for sterile neutrinos and contribute to a full resolution of the Reactor Antineutrino Anomaly, a longstanding puzzle in neutrino physics. By pressing forward on the world's most precise measurement of the \\(^{235}\\)U antineutrino spectrum and measuring the absolute flux of antineutrinos from \\(^{235}\\)U, PROSPECT-II will sharpen a tool with potential value for basic neutrino science, nuclear data validation, and nuclear security applications. Following a two-year deployment at HFIR, an additional PROSPECT-II deployment at a low enriched uranium reactor could make complementary measurements of the neutrino yield from other fission isotopes. PROSPECT-II provides a unique opportunity to continue the study of reactor antineutrinos at short baselines, taking advantage of demonstrated elements of the original PROSPECT design and close access to a highly enriched uranium reactor core.

We measured the cross section of coherent elastic neutrino-nucleus scattering (\\cevns{}) using a CsI[Na] scintillating crystal in a high flux of neutrinos produced at the Spallation Neutron Source (SNS) at Oak Ridge National Laboratory. New data collected before detector decommissioning has more than doubled the dataset since the first observation of \\cevns{}, achieved with this detector. Systematic uncertainties have also been reduced with an updated quenching model, allowing for improved precision. With these analysis improvements, the COHERENT collaboration determined the cross section to be \\((165^{+30}_{-25})\\times10^{-40}\\)~cm\\(^2\\), consistent with the standard model, giving the most precise measurement of \\cevns{} yet. The timing structure of the neutrino beam has been exploited to compare the \\cevns{} cross section from scattering of different neutrino flavors. This result places leading constraints on neutrino non-standard interactions while testing lepton flavor universality and measures the weak mixing angle as \\(\\sin^2\\theta_{W}=0.220^{+0.028}_{-0.026}\\) at \\(Q^2\\approx(50\\text{ MeV})^2\\)

The structure of nuclei around the neutron-rich nucleus 132Sn is of particular interest due to the vicinity of the Z = 50 and N = 82 shell closures and the r-process nucleosynthetic path. Four states in 131Sn with a strong single-particle-like component have previously been studied via the (d,p) reaction, with limited excitation energy resolution. The 130Sn(9Be,8Be)131Sn and 130Sn(13C,12C)131Sn single-neutron transfer reactions were performed in inverse kinematics at the Holifield Radioactive Ion Beam Facility using particle-gamma coincidence spectroscopy. The uncertainties in the energies of the single-particle-like states have been reduced by more than an order of magnitude using the energies of gamma rays. The previous tentative Jpi values have been confirmed. Decays from high-spin states in 131Sn have been observed following transfer on the isomeric component of the 130Sn beam. The improved energies and confirmed spin-parities of the p-wave states important to the r-process lead to direct-semidirect cross-sections for neutron capture on the ground state of 130Sn at 30 keV that are in agreement with previous analyses. A similar assessment of the impact of neutron-transfer on the isomer would require significant nuclear structure and reaction theory input. There are few measurements of transfer reaction on isomers, and this is the first on an isomer in the 132Sn region.