Ge-76 can beta beta decay into three possible excited states of Se-76, with the emission of two or, if the neutrino is Majorana, zero neutrinos. None of these six transitions have yet been observed. The MAJORANA DEMONSTRATOR was designed to study beta beta decay of Ge-76 using a low background array of high purity germanium detectors. With 98.2 kg-y of isotopic exposure, the Demonstrator sets the strongest half-life limits to date for all six transition modes. For 2 nu beta beta to the 0(1)(+) state of Se-76, this search has begun to probe for the first time half-life values predicted using modern many-body nuclear theory techniques, setting a limit of T-1/2 > 1.5 x 10(24) y (90% CL).

The MAJORANA DEMONSTRATOR was an ultra-low-background experiment designed for neutrinoless double-beta decay (0v beta beta) investigation in Ge-76. 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 similar to 88% in Ge-76), 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 x 10(26) yr (90% confidence level) for Ge-76(ppp) -> Cu-73 e(+)pi(+)pi(+) and Ge-76(ppn) -> Zn-73 e(+)pi(+). The partial lifetime limit for the fully inclusive triproton decay mode of Ge-76 is found to be 2.1 x 10(25) yr. Furthermore, we have updated limits for corresponding multinucleon decays.

Abstract The $$2\nu 2\beta $$ 2 ν 2 β decay of $$^{150}\hbox {Nd}$$ 150 Nd to the first excited 740.5 keV $$0^{+}_{1}$$ 0 1 + level of $$^{150}\hbox {Sm}$$ 150 Sm was measured over 5.845 years with the help of a four-crystal low-background HPGe $$\gamma $$ γ spectrometry system in the underground low-background laboratory STELLA of LNGS-INFN. A 2.381 kg highly purified Nd-containing sample was employed as the decay source. The expected de-excitation gamma-quanta of the $$0^{+}_{1}$$ 0 1 + level with energies 334.0 keV and 406.5 keV were observed both in one-dimensional spectrum and in coincidence data resulting in the half-life $$T_{1/2}=[0.83^{+0.18}_{-0.13}\mathrm {(stat)}^{+0.16}_{-0.19}\mathrm {(syst)}]\times 10^{20}$$ T 1 / 2 = [ 0 . 83 - 0.13 + 0.18 ( stat ) - 0.19 + 0.16 ( syst ) ] × 10 20 year. Interpreting an excess of the 334.0-keV peak area as an indication of the $$2\beta $$ 2 β decay of $$^{150}\hbox {Nd}$$ 150 Nd to the 334.0 keV $$2^+_1$$ 2 1 + excited level of $$^{150}\hbox {Sm}$$ 150 Sm with a half-life of $$T_{1/2}=[1.5^{+2.3}_{-0.6}\mathrm {(stat)}\pm 0.4\mathrm {(syst)}]\times 10^{20}$$ T 1 / 2 = [ 1 . 5 - 0.6 + 2.3 ( stat ) ± 0.4 ( syst ) ] × 10 20 year, the $$2\nu 2\beta $$ 2 ν 2 β half-life of $$^{150}\hbox {Nd}$$ 150 Nd for the transition to the 0 $$^{+}_{1}$$ 1 + level is $$T_{1/2}=[1.03^{+0.35}_{-0.22}\mathrm {(stat)}^{+0.16}_{-0.19}\mathrm {(syst)}]\times 10^{20}$$ T 1 / 2 = [ 1 . 03 - 0.22 + 0.35 ( stat ) - 0.19 + 0.16 ( syst ) ] × 10 20 year, in agreement with the previous experiments. Both half-life values reasonably agree with the theoretical calculations in the framework of proton-neutron QRPA with isospin restoration combined with like nucleon QRPA for description of excited states in the final nuclei. For $$2\nu 2\beta $$ 2 ν 2 β and $$0\nu 2\beta $$ 0 ν 2 β transitions of $$^{150}\hbox {Nd}$$ 150 Nd and $$^{148}\hbox {Nd}$$ 148 Nd to several excited levels of $$^{150}\hbox {Sm}$$ 150 Sm and $$^{148}\hbox {Sm}$$ 148 Sm , limits were set at level of $$T_{1/2}>10^{20}-10^{21}$$ T 1 / 2 > 10 20 - 10 21 year.

The SuperNEMO experiment is searching for neutrinoless double-beta-decay of Se-82, with the unique combination of a tracking detector and a segmented calorimeter. This feature allows us to detect the two electrons emitted in the decay and measure their individual energies and angular distribution. The SuperNEMO Demonstrator's calorimeter consists of 712 plastic scintillator blocks read out by large PMTs. Having constructed the calorimeter underground, we performed its first commissioning using gamma-rays from calibration sources or from the ambient radioactivity background. This article presents quality assurance tests of the SuperNEMO Demonstrator's calorimeter, and its first time and energy calibrations with gamma-rays, along with the associated methods. A time alignment of about 120 ps and a time resolution around 615 ps have been achieved. Concerning the energy, an alignment of 7.5% has been obtained. These results will be further improved when associating the tracking detector and detecting electrons from calibration sources.

The 2ν 2β decay of ^150Nd to the first excited 740.5 keV 0^+_1 level of ^150Sm was measured over 5.845 years with the help of a four-crystal low-background HPGe γ spectrometry system in the underground low-background laboratory STELLA of LNGS-INFN. A 2.381 kg highly purified Nd-containing sample was employed as the decay source. The expected de-excitation gamma-quanta of the 0^+_1 level with energies 334.0 keV and 406.5 keV were observed both in one-dimensional spectrum and in coincidence data resulting in the half-life T_1/2=[0.83^+0.18_-0.13(stat)^+0.16_-0.19(syst)]× 10^20 year. Interpreting an excess of the 334.0-keV peak area as an indication of the 2β decay of ^150Nd to the 334.0 keV 2^+_1 excited level of ^150Sm with a half-life of T_1/2=[1.5^+2.3_-0.6(stat)± 0.4(syst)]× 10^20 year, the 2ν 2β half-life of ^150Nd for the transition to the 0 ^+_1 level is T_1/2=[1.03^+0.35_-0.22(stat)^+0.16_-0.19(syst)]× 10^20 year, in agreement with the previous experiments. Both half-life values reasonably agree with the theoretical calculations in the framework of proton-neutron QRPA with isospin restoration combined with like nucleon QRPA for description of excited states in the final nuclei. For 2ν 2β and 0ν 2β transitions of ^150Nd and ^148Nd to several excited levels of ^150Sm and ^148Sm , limits were set at level of T_1/2>10^20-10^21 year.

With excellent energy resolution and ultralow-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 ν_{s}→ν_{a}. We report new limits on fermionic dark matter absorption (χ+A→ν+A) and sub-GeV DM-nucleus 3→2 scattering (χ+χ+A→ϕ+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.

Potential-induced degradation is a significant issue affecting the performance and reliability of photovoltaic systems, particularly in large-scale installations. Understanding the mechanisms underlying the formation of potential-induced degradation is crucial for developing effective mitigation strategies and ensuring the long-term sustainability of solar energy technologies. During the inspection of a 1.2 MWp photovoltaic power plant, various imaging methods, electrical measurements, spectroscopic characterization methods, and monitoring data analyses were utilized and combined. We observed that two percent of the photovoltaic modules at the string ends exhibited the characteristic checkerboard pattern in infrared or electroluminescence imaging, implicating issues on twelve percent of all strings. This uneven distribution of potential-induced degradation-affected modules suggests additional key factors are at play. Investigations of the backsheet and ethylene-vinyl acetate using near-infrared reflectance analysis revealed that one backsheet type and two different ethylene-vinyl acetate types were present in the installed solar panels. Yet, only one type of ethylene-vinyl acetate correlated with potential-induced degradation. The same type also exhibited a higher rate of oxidative degradation. Scanning electron microscopy and energy-dispersive X-ray spectroscopy revealed a significantly increased sodium ion content in the ethylene-vinyl acetate and glass of the potential-induced degradation-affected modules. Our findings highlight the crucial role of polymer encapsulation in the development of potential-induced degradation and underscore the importance of careful polymer selection in the design of photovoltaic module technologies.

The CROSS experiment will search for neutrinoless double-beta decay using a specific mechanical structure to hold thermal detectors. The design of the structure was tuned to minimize the background contribution, keeping an optimal detector performance. A single module of the structure holds two scintillating bolometers (with a crystal size of 45 x 45 x 45 mm and a Ge slab facing the crystal's upper side) in the Cu frame, allowing for a modular construction of a large-scale array. Two designs are released: the initial Thick version contains around 15% of Cu over the crystal mass (lithium molybdate, LMO), while this ratio is reduced to similar to 6% in a finer ( Slim ) design. Both designs were tested extensively at aboveground (IJCLab, France) and underground (LSC, Spain) laboratories. In particular, at LSC we used a pulse-tube-based CROSS facility to operate a 6-crystal array of LMOs enriched/depleted in Mo-100. The tested LMOs show high spectrometric performance in both designs; notably, the measured energy resolution is 5-7 keV FWHM at 2615 keV gamma s, nearby the Q-value of Mo-100 (3034 keV). Due to the absence of a reflective cavity around LMOs, a low scintillation signal is detected by Ge bolometers: similar to 0.3 keV (150 photons) for 1-MeV gamma(beta) LMO-event. Despite that, an acceptable separation between alpha and gamma(beta) events is achieved with most devices. The highest efficiency is reached with light detectors in the Thick design thanks to a lower baseline noise width (0.05-0.09 keV RMS) when compared to that obtained in the Slim version (0.10-0.35 keV RMS). Given the pivotal role of bolometric photodetectors for particle identification and random coincidences rejection, we will use the structure here described with upgraded light detectors, featuring thermal signal amplification via the Neganov-Trofimov-Luke effect, as also demonstrated in the present work.

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 MAJORANA DEMONSTRATOR 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 ->nu(e)nu(e)(sic)nu(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 current experiments searching for neutrinoless double- β ( 0νββ ) decay also collect large statistics of Standard Model allowed two-neutrino double- β ( 2νββ ) decay events. These can be used to search for Beyond Standard Model (BSM) physics via 2νββ decay spectral distortions. 100Mo has a natural advantage due to its relatively short half-life, allowing higher 2νββ decay statistics at equal exposures compared to the other isotopes. We demonstrate the potential of the dual read-out bolometric technique exploiting a 100Mo exposure of 1.47 kg × years, acquired in the CUPID-Mo experiment at the Modane underground laboratory (France). We set limits on 0νββ decays with the emission of one or more Majorons, on 2νββ decay with Lorentz violation, and 2νββ decay with a sterile neutrino emission. In this analysis, we investigate the systematic uncertainty induced by modeling the 2νββ decay spectral shape parameterized through an improved model, an effect never considered before. This work motivates searches for BSM processes in the upcoming CUPID experiment, which will collect the largest amount of 2νββ decay events among the next-generation experiments.

The background index (BI) is an important quantity to project and calculate the half-life sensitivity of neutrinoless double-beta decay (0 nu beta beta) 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 Ge-76 to search for 0 nu beta beta. 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] x 10(-4) cts/(keV kg yr) from the Th-232 and U-238 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.

Abstract The current experiments searching for neutrinoless double- $$\beta $$ β ( $$0\nu \beta \beta $$ 0 ν β β ) decay also collect large statistics of Standard Model allowed two-neutrino double- $$\beta $$ β ( $$2\nu \beta \beta $$ 2 ν β β ) decay events. These can be used to search for Beyond Standard Model (BSM) physics via $$2\nu \beta \beta $$ 2 ν β β decay spectral distortions. 100Mo has a natural advantage due to its relatively short half-life, allowing higher $$2\nu \beta \beta $$ 2 ν β β decay statistics at equal exposures compared to the other isotopes. We demonstrate the potential of the dual read-out bolometric technique exploiting a 100Mo exposure of 1.47 kg $$\times $$ × years, acquired in the CUPID-Mo experiment at the Modane underground laboratory (France). We set limits on $$0\nu \beta \beta $$ 0 ν β β decays with the emission of one or more Majorons, on $$2\nu \beta \beta $$ 2 ν β β decay with Lorentz violation, and $$2\nu \beta \beta $$ 2 ν β β decay with a sterile neutrino emission. In this analysis, we investigate the systematic uncertainty induced by modeling the $$2\nu \beta \beta $$ 2 ν β β decay spectral shape parameterized through an improved model, an effect never considered before. This work motivates searches for BSM processes in the upcoming CUPID experiment, which will collect the largest amount of $$2\nu \beta \beta $$ 2 ν β β decay events among the next-generation experiments.

We report on the development of thermal detectors based on large-size tellurium dioxide crystals (45 x 45 x 45 mm), containing tellurium enriched in 130 Te to about 91%, for the CROSS double-beta decay experiment. A powder used for the crystals growth was additionally purified by the directional solidification method, resulting in the reduction of the concentration of impurities by a factor 10, to a few ppm of the total concentration of residual elements (the main impurity is Fe). The purest part of the ingot (the first 200 mm, about 80% of the total length of the cylindrical part of the ingot) was determined by scanning segregation profiles of impurities and used for the 130 TeO 2 powder production with no evidence of re-contamination. The crystal growth was verified with precursors produced from a powder with natural Te isotopic composition, and two small-size (20 x 20 x 10 mm) samples were tested at a sea-level laboratory showing high bolometric and spectrometric performance together with acceptable 210 Po content (below 10 mBq/kg). This growth method was then applied for the production of six large cubic 130 TeO 2 crystals and 4 of them were taken randomly to be characterized at the Canfranc underground laboratory, in the CROSS-dedicated low-background cryogenic facility. Two 130 TeO 2 samples were coated with a thin, O (100 nm), metal film in form of Al layer (on 4 sides) or AlPd grid (on a single side) to investigate the possibility to tag surface events by pulse-shape discrimination. Similarly to the small natural precursors, large-volume 130 TeO 2 bolometers show high performance and even better internal purity (210Po 210 Po activity 1 mBq/kg, while activities of 228 Th and 226 Ra are below 0.01 mBq/kg), satisfying requirements for the CROSS and, potentially, next-generation experiments.

CUPID-Mo, located in the Laboratoire Souterrain de Modane (France), was a demonstrator for the next generation 0νββ decay experiment, CUPID. It consisted of an array of 20 enriched Li _2 ^100 MoO _4 bolometers and 20 Ge light detectors and has demonstrated that the technology of scintillating bolometers with particle identification capabilities is mature. Furthermore, CUPID-Mo can inform and validate the background prediction for CUPID. In this paper, we present a detailed model of the CUPID-Mo backgrounds. This model is able to describe well the features of the experimental data and enables studies of the 2νββ decay and other processes with high precision. We also measure the radio-purity of the Li _2 ^100 MoO _4 crystals which are found to be sufficient for the CUPID goals. Finally, we also obtain a background index in the region of interest of 3.7 ^+0.9_-0.8 (stat) ^+1.5_-0.7 (syst) × 10 ^-3 counts/ Δ E_FWHM/mol_iso/year, the lowest in a bolometric 0νββ decay experiment.

AbstractThe NEMO-3 results for the double-$$\beta $$ β decay of $$^{150}$$ 150 Nd to the 0$$^+_1$$ 1 + and 2$$^+_1$$ 1 + excited states of $$^{150}$$ 150 Sm are reported. The data recorded during 5.25 year with 36.6 g of the isotope $$^{150}$$ 150 Nd are used in the analysis. The signal of the $$2\nu \beta \beta $$ 2 ν β β transition to the 0$$^+_1$$ 1 + excited state is detected with a statistical significance exceeding 5$$\sigma $$ σ . The half-life is measured to be $$T_{1/2}^{2\nu \beta \beta }(0^+_1) = \left[ 1.11 ^{+0.19}_{-0.14} \,\left( \hbox {stat}\right) ^{+0.17}_{-0.15}\,\left( \hbox {syst}\right) \right] \times 10^{20}$$ T 1 / 2 2 ν β β ( 0 1 + ) = 1 . 11 - 0.14 + 0.19 stat - 0.15 + 0.17 syst × 10 20 year, which is the most precise value that has been measured to date. 90% confidence-level limits are set for the other decay modes. For the $$2\nu \beta \beta $$ 2 ν β β decay to the 2$$^+_1$$ 1 + level the limit is $$T^{2\nu \beta \beta }_{1/2}(2^+_1) > 2.42 \times 10^{20}~\hbox {year}$$ T 1 / 2 2 ν β β ( 2 1 + ) > 2.42 × 10 20 year . The limits on the $$0\nu \beta \beta $$ 0 ν β β decay to the 0$$^+_1$$ 1 + and 2$$^+_1$$ 1 + levels of $$^{150}$$ 150 Sm are significantly improved to $$T_{1/2}^{0\nu \beta \beta }(0^+_1) > 1.36 \times 10^{22}~\hbox {year}$$ T 1 / 2 0 ν β β ( 0 1 + ) > 1.36 × 10 22 year and $$T_{1/2}^{0\nu \beta \beta }(2^+_1) > 1.26 \times 10^{22}~\hbox {year}$$ T 1 / 2 0 ν β β ( 2 1 + ) > 1.26 × 10 22 year .

The CUPID-Mo experiment, located at the Laboratoire Souterrain de Modane (France), was a demonstrator experiment for CUPID. It consisted of an array of 20 Li-2 Mo-100 O-4 (LMO) calorimeters, each equipped with a Ge light detector for particle identification. In this work, we present the result of a search for two-neutrino and neutrinoless double-beta decays of Mo-100 to the first 0(+) and 2(+) excited states of Ru-100 using the full CUPID-Mo exposure (2.71 kg yr of LMO). We measure the half-life of 2 nu beta beta decay to the 0(1)(+) state as T-1/2(2 nu -> 01+) = (7.5 +/- 1 0.8 (stat.)(-0.3)(+0.4) (syst.)) x 10(20) yr. The bolometric technique enables measurement of the electron energies as well as the gamma rays from nuclear deexcitation and this allows us to set new limits on the two-neutrino decay to the 2(1)(+) state of T-1/2(2 nu -> 21+) > 4.4 x 10(21) yr (90% c.i.) and on the neutrinoless modes of T-1/2(0 nu -> 21+) > 2.1 x 10(23) yr (90% c.i.), T-1/2(0 nu -> 01+) > 1.2 x 10(23) yr (90% c.i.). Information on the electrons' spectral shape is obtained, which allows us to 1 make the first comparison of the single and higher state dominance 2 nu beta beta decay models for the 0(1)(+) excited state of Ru-100.

Neutrinoless double beta decay (0νββ) is a yet unobserved nuclear process that would demonstrate Lepton number violation, a clear evidence of beyond standard model physics. The process two neutrino double beta decay (2νββ) is allowed by the standard model and has been measured in numerous experiments. In this Letter, we report a measurement of 2νββ decay half-life of ^{100}Mo to the ground state of ^{100}Ru of [7.07±0.02(stat)±0.11(syst)]×10^{18}  yr by the CUPID-Mo experiment. With a relative precision of ±1.6% this is the most precise measurement to date of a 2νββ decay rate in ^{100}Mo. In addition, we constrain higher-order corrections to the spectral shape, which provides complementary nuclear structure information. We report a novel measurement of the shape factor ξ_{3,1}=0.45±0.03(stat)±0.05(syst) based on a constraint on the ratio of higher-order terms from theory, which can be reliably calculated. This is compared to theoretical predictions for different nuclear models. We also extract the first value for the effective axial vector coupling constant obtained from a spectral shape study of 2νββ decay.

^{180m}Ta is a rare nuclear isomer whose decay has never been observed. Its remarkably long lifetime surpasses the half-lives of all other known β and electron capture decays due to the large K-spin differences and small energy differences between the isomeric and lower-energy states. Detecting its decay presents a significant experimental challenge but could shed light on neutrino-induced nucleosynthesis mechanisms, the nature of dark matter, and K-spin violation. For this study, we repurposed the Majorana Demonstrator, an experimental search for the neutrinoless double-beta decay of ^{76}Ge using an array of high-purity germanium detectors, to search for the decay of ^{180m}Ta. More than 17 kg, the largest amount of tantalum metal ever used for such a search, was installed within the ultralow-background detector array. In this Letter, we present results from the first year of Ta data taking and provide an updated limit for the ^{180m}Ta half-life on the different decay channels. With new limits up to 1.5×10^{19}  yr, we improved existing limits by 1-2 orders of magnitude which are the most sensitive searches for a single β and electron capture decay ever achieved. Over all channels, the decay can be excluded for T_{1/2}<0.29×10^{18}  yr.

The NEMO-3 results for the double- β decay of ^150 Nd to the 0 ^+_1 and 2 ^+_1 excited states of ^150 Sm are reported. The data recorded during 5.25 year with 36.6 g of the isotope ^150 Nd are used in the analysis. The signal of the 2νββ transition to the 0 ^+_1 excited state is detected with a statistical significance exceeding 5 σ . The half-life is measured to be T_1/2^2νββ(0^+_1) = [ 1.11 ^+0.19_-0.14 ( stat) ^+0.17_-0.15 ( syst) ] × 10^20 year, which is the most precise value that has been measured to date. 90 2νββ decay to the 2 ^+_1 level the limit is T^2νββ_1/2(2^+_1) > 2.42 × 10^20 year . The limits on the 0νββ decay to the 0 ^+_1 and 2 ^+_1 levels of ^150 Sm are significantly improved to T_1/2^0νββ(0^+_1) > 1.36 × 10^22 year and T_1/2^0νββ(2^+_1) > 1.26 × 10^22 year .

An array of twelve 0.28 kg lithium molybdate (LMO) low-temperature bolometers equipped with 16 bolometric Ge light detectors, aiming at optimization of detector structure for CROSS and CUPID double-beta decay experiments, was constructed and tested in a low-background pulse-tube-based cryostat at the Canfranc underground laboratory in Spain. Performance of the scintillating bolometers was studied depending on the size of phonon NTD-Ge sensors glued to both LMO and Ge absorbers, shape of the Ge light detectors (circular vs. square, from two suppliers), in different light collection conditions (with and without reflector, with aluminum coated LMO crystal surface). The scintillating bolometer array was operated over 8 months in the low-background conditions that allowed to probe a very low, μBq/kg, level of the LMO crystals radioactive contamination by ^228Th and ^226Ra.