A search for alpha and beta beta decays of naturally occurring osmium isotopes to the excited levels of daughter nuclei has been performed using an ultra-low-background broad-energy germanium gamma detector and an ultrapure osmium sample at the Gran Sasso National Laboratory of the INFN (Italy). The isotopic composition of the osmium sample has been measured with high precision by using negative thermal ionization mass spectrometry. During the data taking with the gamma detector, no effect has been detected, and lower limits for the half-life of alpha and beta beta decays were set at the level of 10(15) - 10(20) yr. In the case of a decays of Os-184 and Os-186 to the first excited levels of daughter nuclei, the limits substantially exceed the present theoretical estimates of the decays probabilities. This gives hope to the possibility to detect such transitions in the ongoing data taking. The present work will describe a review of recent new measurements and new experimental perspectives.

Abstract The AMoRE collaboration searches for neutrinoless double beta decay of $$^{100}$$ 100 Mo using molybdate scintillating crystals via low temperature thermal calorimetric detection. The early phases of the experiment, AMoRE-pilot and AMoRE-I, have demonstrated competitive discovery potential. Presently, the AMoRE-II experiment, featuring a large detector array with about 90 kg of $$^{100}$$ 100 Mo isotope, is under construction. This paper discusses the baseline design and characterization of the lithium molybdate cryogenic calorimeters to be used in the AMoRE-II detector modules. The results from prototype setups that incorporate new housing structures and two different crystal masses (316 g and 517–521 g), operated at 10 mK temperature, show energy resolutions (FWHM) of 7.55–8.82 keV at the 2.615 MeV $$^{208}$$ 208 Tl $$\gamma $$ γ line and effective light detection of 0.79–0.96 keV/MeV. The simultaneous heat and light detection enables clear separation of alpha particles with a discrimination power of 12.37–19.50 at the energy region around $$^{6}$$ 6 Li $$(n,\alpha )^3$$ ( n , α ) 3 H with Q-value = 4.785 MeV. Promising detector performances were demonstrated at temperatures as high as 30 mK, which relaxes the temperature constraints for operating the large AMoRE-II array.

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.

AbstractAMoRE-II aims to search for neutrinoless double beta decay ($$0\nu \beta \beta $$ 0 ν β β ) with an array of 423 $$\hbox {Li}_2^{100}\hbox {MoO}_4$$ Li 2 100 MoO 4 crystals operating in the cryogenic system as the main phase of the Advanced Molybdenum-based Rare process Experiment (AMoRE). AMoRE has been planned to operate in three phases: AMoRE-pilot, AMoRE-I, and AMoRE-II. AMoRE-II is currently being installed at the Yemi Underground Laboratory, located approximately 1000 m deep in Jeongseon, Korea. The goal of the experiment is to reach an exclusion half-life sensitivity to the $$0\nu \beta \beta $$ 0 ν β β of $$^{100}$$ 100 Mo on the level of $$T^{0\nu \beta \beta }_{1/2} > 6 \times 10^{26}$$ T 1 / 2 0 ν β β > 6 × 10 26 year that covers completely the inverted Majorana neutrino mass hierarchy region of (15–46) meV. To achieve this, the background level of the experimental configurations and possible background sources of gamma and beta events should be well understood. We have intensively performed Monte Carlo simulations using the GEANT4 toolkit in all the experimental configurations with potential sources. We report the estimated background level that meets the $$10^{-4}$$ 10 - 4 counts/(keV$$\cdot $$ · kg$$\cdot $$ · year) requirement for AMoRE-II in the Region Of Interest (ROI) and show the projected half-life sensitivity based on the simulation study.

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.

In the following, the first measurement of CNO solar neutrinos obtained by Borexino by exploiting the directional information retained by solar neutrino is summarized [1]. The Correlated Integrated Directionality (CID) method makes use of the sub-dominant Cherenkov light emitted by the Borexino liquid scintillator to correlate between the first few detected photons in each event and the known position of the Sun for each event and, therefore, to discriminate between the signal and the radioactive background on a statistical basis. By applying this technique to the complete 2007-2021 Borexino dataset, the hypothesis of no CNO neutrinos is rejected with > 5 sigma posterior probability, without making use of any information on the background levels in the scintillator.

BINGO is a project aiming to set the grounds for large-scale bolometric neutrinoless double-beta-decay experiments capable of investigating the effective Majorana neutrino mass at a few meV level. It focuses on developing innovative technologies (a detector assembly, cryogenic photodetectors and active veto) to achieve a very low background index, of the order of 10 -5 counts/(keV kg yr) in the region of interest. The BINGO demonstrator, called MINI-BINGO, is designed to investigate the promising double-beta-decay isotopes 100 Mo and 130 Te and it will be composed of Li2MoO4 and TeO2 crystals coupled to bolometric light detectors and surrounded by a Bi4Ge3O12-based veto. This will allow us to reject a significant background in bolometers caused by surface contamination from a-active radionuclides by means of light yield selection and to mitigate other sources of background, such as surface contamination from ,3-active radionuclides, external y radioactivity, and pile-up due to random coincidence of background events. This paper describes an R&D program towards the BINGO goals, particularly focusing on the development of an innovative assembly designed to reduce the passive materials within the line of sight of the detectors, which is expected to be a dominant source of background in next-generation bolometric experiments. We present the performance of two prototype modules - housing four cubic (4.5-cm side) Li2MoO4 crystals in total - operated in the Canfranc underground laboratory in Spain within a facility developed for the CROSS double-beta-decay experiment.

The AMoRE-II experiment will search for the 0νββ decay of 100Mo nuclei using molybdate crystal scintillators, operating at milli-Kelvin (mK) temperatures, with a total of 80 kg of 100Mo. The background goal for the experiment is 10–4 counts/keV/kg/year in the region of interest around the 0νββ decay Q-value of 3,034 keV. To achieve this level, the rate of background signals arising from emissions produced by decays of radioactive impurities in the detector and shielding materials must be strictly controlled. To do this, concentrations of such impurities are measured and are controlled through materials selection and purification. In this paper, we describe the design and the construction materials used to build the AMoRE-II detector and shielding system, including active and passive shielding, the cryostat, and the detector holders and instrumentation, and we report on measurements of radioactive impurities within candidate and selected materials.

Borexino, placed at LNGS in Italy, was a 280-ton liquid scintillator detector that took data from May 2007 to October 2021. Thanks to its unprecedented radio-purity, the real time spectroscopic measurement of solar neutrinos from both the pp-chain and Carbon-Nitrogen-Oxygen (CNO) fusion cycle of the Sun has been performed. Borexino also reported the first directional measurement of sub-MeV Be-7 solar neutrinos with the Phase-I period (May 2007-May 2010) using a novel technique called Correlated and Integrated Directionality (CID), exploiting the sub-dominant and directional Cherenkov photons detected at early times. For the first time, we provide the CNO solar neutrinos measurement without using an independent constraint on Bi-210 background rate by exploiting the CID technique on the complete Borexino detector live time dataset. This article presents the complete analysis strategy and the latest results on CNO solar neutrinos obtained by using the CID technique in Borexino. In addition, we also present the most precise CNO measurement obtained by Borexino using a spectral fit on the Phase-III dataset as used in 2022 analysis, where the novel CID result is now applied as an additional constraint.

Borexino could efficiently distinguish between α and β radiation in its liquid scintillator by the characteristic time profile of its scintillation pulse. This α/β discrimination, first demonstrated on the ton scale in the counting test facility prototype, was used throughout the lifetime of the experiment between 2007 and 2021. With this method, the α events are identified and subtracted from the solar neutrino events similar to β. This is particularly important in liquid scintillators, as the α scintillation is strongly quenched. In Borexino, the prominent Po210 decay peak was a background in the energy range of electrons scattered from Be7 solar neutrinos. Optimal α/β discrimination was achieved with a , with a higher ability to leverage the timing information of the scintillation photons detected by the photomultiplier tubes. An event-by-event, high efficiency, stable, and uniform pulse shape discrimination was essential in characterizing the spatial distribution of background in the detector. This benefited most Borexino measurements, including solar neutrinos in the pp chain and the first direct observation of the CNO cycle in the Sun. This paper presents key milestones in α/β discrimination in Borexino as a term of comparison for current and future large liquid scintillator detectors. Published by the American Physical Society 2024

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.

A long-term measurement was conducted to search for α, double-α and double-β decays with γ quanta emission in naturally occurring osmium isotopes. This study took advantage of two ultra-low background HPGe detectors and one ultra-low background BEGe detector at the Gran Sasso National Laboratory (LNGS) of the INFN. Over almost 5 years of data were taken using high-purity osmium samples of approximately 173 g. The half-life limits set for α decays of 184Os to the first 2+ 103.6 keV excited level of 180W (T1/2 ≥ 9.3 × 1015 yr) and of 186Os to the first 2+ 100.1 keV of 182W (T1/2 ≥ 4.8 × 1017 yr) exceed substantially the present theoretical predictions that are at level of T1/2 (0.6–3) × 1015 yr for 184Os and T1/2 (0.3–2) × 1017 yr for 186Os. New half-life limits on the 2EC and ECβ+ decay of 184Os to the ground and excited levels of 184W were set at level of T1/2 > 1016–1017 yr; a lower limit on the 2β– decay of 192Os to the 2+ 316.5 keV excited level of 192Pt was estimated as T1/2 ≥ 6.1 × 1020 yr. The half-life limits for 2α decay of 189Os and 192Os were set for the first time at level of T1/2 > 1020 yr.

Brief biography and scientific achievements of Yuri Georgiiovych Zdesenko in relation with his 80-th anniversary.

We report a study on the background of the Advanced Molybdenum-Based Rare process Experiment (AMoRE), a search for neutrinoless double beta decay (\znbb) of $^{100}$Mo. The pilot stage of the experiment was conducted using $\sim$1.9 kg of \CAMOO~ crystals at the Yangyang Underground Laboratory, South Korea, from 2015 to 2018. We compared the measured $\beta/\gamma$ energy spectra in three experimental configurations with the results of Monte Carlo simulations and identified the background sources in each configuration. We replaced several detector components and enhanced the neutron shielding to lower the background level between configurations. A limit on the half-life of $0\nu\beta\beta$ decay of $^{100}$Mo was found at $T_{1/2}^{0\nu} \ge 3.0\times 10^{23}$ years at 90\% confidence level, based on the measured background and its modeling. Further reduction of the background rate in the AMoRE-I and AMoRE-II are discussed.

Highly forbidden β decays provide a sensitive test to nuclear models in a regime in which the decay goes through high spin-multipole states, similar to the neutrinoless double- β decay process. There are only 3 nuclei (50V, 113Cd, 115In) which undergo a 4^th forbidden non-unique β decay. In this work, we compare the experimental 113Cd spectrum to theoretical spectral shapes in the framework of the spectrum-shape method. We measured with high precision, with the lowest energy threshold and the best energy resolution ever, the β spectrum of 113Cd embedded in a 0.43 kg CdWO_4 crystal, operated over 26 days as a bolometer at low temperature in the Canfranc underground laboratory (Spain). We performed a Bayesian fit of the experimental data to three nuclear models (IBFM-2, MQPM and NSM) allowing the reconstruction of the spectral shape as well as the half-life. The fit has two free parameters, one of which is the effective weak axial-vector coupling constant, g_A^eff , which resulted in g_A^eff between 1.0 and 1.2, compatible with a possible quenching. Based on the fit, we measured the half-life of the 113Cd β decay including systematic uncertainties as 7.73^+0.60_-0.57× 10^15 yr, in agreement with the previous experiments. These results represent a significant step towards a better understanding of low-energy nuclear processes.

The recent observation of CNO solar neutrinos by Borexino (BX) has proven the high potential offered by large underground ultrapure liquid scintillators to disclose weak neutrino and antineutrino fluxes. Supernovae explosions, gamma-ray bursts, solar flares and Gravitational Waves (GW) are among the possible extra-terrestrial sources of neutrinos and antineutrinos. The extreme radiopurity of the BX detector has already allowed to get the best upper limits on all flavor fluences in the few MeV energy range from gamma ray bursts, to set limits on the diffuse supernova antineutrino background in the unexplored energy region below 8 MeV and to get the strongest upper limits on fast radio bursts associated neutrino fluences up to 50 MeV. Recently, BX has searched for neutrino events in correlation with GW events from 2015 to 2020 using the BX data-set of the same periods. The strongest upper limits on GW-associated neutrino and antineutrino fluences have been obtained in the (0.5 - 5.0) MeV neutrino energy range. The present contribution is aimed to describe the analysis procedures and the deduced upper limits for all neutrino flavors.

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.

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.