Search

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.

Abstract Rare-event search experiments located on-surface, such as short-baseline reactor neutrino experiments, are often limited by muon-induced background events. Highly efficient muon vetos are essential to reduce the detector background and to reach the sensitivity goals. We demonstrate the feasibility of deploying organic plastic scintillators at sub-Kelvin temperatures. For the NUCLEUS experiment, we developed a cryogenic muon veto equipped with wavelength shifting fibers and a silicon photo multiplier operating inside a dilution refrigerator. The achievable compactness of cryostat-internal integration is a key factor in keeping the muon rate to a minimum while maximizing coverage. The thermal and light output properties of a plastic scintillation detector were examined. We report first data on the thermal conductivity and heat capacity of the polystyrene-based scintillator UPS-923A over a wide range of temperatures extending below one Kelvin. The light output was measured down to 0.8 K and observed to increase by a factor of 1.61 ± 0.05 compared to 300 K. The development of an organic plastic scintillation muon veto operating in sub-Kelvin temperature environments opens new perspectives for rare-event searches with cryogenic detectors at sites lacking substantial overburden.

An experiment to search for 2ε-, εβ+- and 2β+-decays of 106Cd, using a 215 g cadmium tungstate scintillation crystal enriched at 66 % by 106Cd (106CdWO4) is carried out at the Gran Sasso underground laboratory (Italy). Events in the 106CdWO4 detector are recorded in (anti)coincidences with two large-volume CdWO4 scintillation counters. The design of the detector system, calibration and background measurements, methods, and results of data analysis to determine key detector characteristics are described. The experimental data are compared with Monte Carlo simulation results, and a background model is constructed. The radioactive contamination of the setup components is studied. The sensitivity of the experiment approaches the level of theoretical predictions for the 2νεβ+-decay channel, while for other possible 2β-decay channels it is already on the level of lim T1/2 ∼ 1021-1022 years.

The long-standing model-independent annual modulation effect measured by DAMA deep underground at Gran Sasso Laboratory with different experimental configurations is summarized and perspectives will be highlighted. DAMA/LIBRA-phase2 set-up, $\simeq$ 250 kg highly radio-pure NaI(Tl) confirms the evidence of a signal that meets all the requirements of the model independent Dark Matter annual modulation signature at high C.L.; the full exposure is 2.86 ton $\times$ yr over 22 annual cycles. The experiment is currently collecting data in the DAMA/LIBRA-phase2 empowered configuration with an even lower software energy threshold. Other recent claims are shortly commented.

The NUCLEUS experiment aims to perform a high-precision measurement of Coherent Elastic Neutrino-Nucleus Scattering (CEvNS) at the EdF Chooz B nuclear power plant in France. CEvNS is a unique process to study neutrino properties and to search for physics beyond the Standard Model. The study of CEvNS is also important for light Dark-Matter searches. It could be a possible irreducible background for high-sensitivity Dark-Matter experiments. NUCLEUS is an experiment under construction based on ultra-low threshold ($\sim$20 eV$_{nr}$) cryogenic calorimeters, operated at tens-of-mK temperatures.

Many low-threshold experiments observe sharply rising event rates of yet unknown origins below a few hundred eV, and larger than expected from known backgrounds. Due to the significant impact of this excess on the dark matter or neutrino sensitivity of these experiments, a collective effort has been started to share the knowledge about the individual observations. For this, the EXCESS Workshop was initiated. In its first iteration in June 2021, ten rare event search collaborations contributed to this initiative via talks and discussions. The contributing collaborations were CONNIE, CRESST, DAMIC, EDELWEISS, MINER, NEWS-G, NUCLEUS, RICOCHET, SENSEI and SuperCDMS. They presented data about their observed energy spectra and known backgrounds together with details about the respective measurements. In this paper, we summarize the presented information and give a comprehensive overview of the similarities and differences between the distinct measurements. The provided data is furthermore publicly available on the workshop’s data repository together with a plotting tool for visualization.

Any experiment aiming to measure rare events, like Coherent Elastic neutrino-Nucleus Scattering (CE ν NS) or hypothetical Dark Matter scattering, via nuclear recoils in cryogenic detectors relies crucially on a precise detector calibration at sub-keV energies. The Crab collaboration developed a new calibration technique based on the capture of thermal neutrons inside the target crystal. Together with the Nucleus experiment, first measurements with a moderated 252 Cf neutron source and a cryogenic CaWO 4 detector were taken. We observed for the first time the 112eV peak caused by the 182 W(n, γ ) 183 W capture reaction and subsequent nuclear recoils. Currently, Crab is preparing a precision measurement campaign based on a monochromatic flux of thermal neutrons from the 250-kW Triga-mark II nuclear reactor at TU Wien. In this contribution, we introduce the Crab technique, present the first measurement of the 112eV peak, report the preparations for the precision measurement campaign, and give an outlook on the impact on the field of cryogenic detectors., Competing Interests: Conflict of interestThe authors have no relevant financial or non-financial interests to disclose., (© The Author(s) 2024.)

Coherent elastic neutrino-nucleus scattering and low-mass dark matter detectors rely crucially on the understanding of their response to nuclear recoils. We report the first observation of a nuclear recoil peak at around 112 eV induced by neutron capture. The measurement was performed with a CaWO_{4} cryogenic detector from the NUCLEUS experiment exposed to a ^{252}Cf source placed in a compact moderator. We identify the expected peak structure from the single-γ de-excitation of ^{183}W with 3σ and its origin by neutron capture with 6σ significance. This result demonstrates a new method for precise, in situ, and nonintrusive calibration of low-threshold experiments.