Search

A long-term measurement was conducted to search for $\alpha$, double-$\alpha$ and double-$\beta$ decays with $\gamma$ 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 a decays of $^{184}$Os to the first $2^+$ 103.6 keV excited level of $^{180}$W ($T_{1/2} > 9.3 \times 10^{15}$ yr) and of $^{186}$Os to the first $2^+$ 100.1 keV of $^{182}$W ($T_{1/2} > 4.8 \times 10^{17}$ yr) exceed substantially the present theoretical predictions that are at level of $T_{1/2} \sim (0.6 - 3) \times 10^{15}$ yr for $^{184}$Os and $T_{1/2} \sim (0.3 - 2) \times 10^{17}$ yr for $^{186}$Os. New half-life limits on the 2EC and EC$\beta^+$ decay of $^{184}$Os to the ground and excited levels of $^{184}$W were set at level of $T_{1/2} > 10^{16} - 10^{17}$ yr; a lower limit on the $2\beta^-$ decay of $^{192}$Os to the $2^+$ 316.5 keV excited level of $^{192}$Pt was estimated as $T_{1/2} > 6.1 \times 10^{20}$ yr. The half-life limits for $2\alpha$ decay of $^{189}$Os and $^{192}$Os were set for the first time at level of $T_{1/2} > 10^{20}$ yr., Comment: 38 pages, 17 figures, 5 tables

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 0.8K and observed to increase by a factor of 1.61$\pm$0.05 compared to 300K. 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.

The emission of $\gamma$-rays after a neutron capture in a cryogenic detector can generate mono-energetic nuclear recoils in the sub-keV regime, of direct interest for the calibration of Dark Matter and Coherent Elastic Neutrino Nucleus Scattering experiments. Here we show that accurate predictions of the nuclear recoil spectra induced by neutron captures require taking into account the interplay between the development in time of the de-excitation $\gamma$-cascade of the target nucleus and that of the associated atomic collisions in matter. We present detailed simulations coupling the FIFRELIN code for the description of the $\gamma$-cascades and the IRADINA code for the modelling of the fast atomic movements in matter. Nuclear recoil spectra are predicted, and made available to the community, for concrete cases of Al$_2$O$_3$, Si, Ge and CaWO$_4$ crystals exposed to a low intensity beam of thermal neutrons. We find that timing effects cause new calibration peaks to emerge in the recoil spectra and also impact the shape of the continuous recoil distribution. We discuss how they could give access to a rich physics program, spanning the accurate study of the response of cryogenic detectors in the sub-keV range, tests of solid state physics simulations and tests of nuclear models.

Proceedings for our meeting ``What comes beyond the Standard Models'', which covered a broad series of subjects., Comment: This is the proceedings for the 25th Workshop in Bled for "What comes beyond the Standard Models'' including also a webinar "meeting'' using Cosmovia on the same subject

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 searches. NUCLEUS is an experiment under construction based on ultra-low threshold (20 eVnr) cryogenic calorimeters, operated at tens-of-mK temperatures., Comment: Procceding for 14th International Conference on Identification of Dark Matter Vienna, Austria, 18-22 July 2022 - Submitted to SciPost

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. The measured spectrum is found in agreement with simulations and the expected peak structure from the single-$\gamma$ de-excitation of $^{183}$W is identified with 3 $\sigma$ significance. This result demonstrates a new method for precise, in-situ, and non-intrusive calibration of low-threshold experiments.

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., Comment: Proceedings of IDM 2022, July 18-22, 2022. A Section is dedicated to rebut the arguments of arXiv:2208.05158

Coherent elastic neutrino-nucleus scattering (CE$\nu$NS) is a process in which neutrinos scatter on a nucleus which acts as a single particle. Though the total cross section is large by neutrino standards, CE$\nu$NS has long proven difficult to detect, since the deposited energy into the nucleus is $\sim$ keV. In 2017, the COHERENT collaboration announced the detection of CE$\nu$NS using a stopped-pion source with CsI detectors, followed up the detection of CE$\nu$NS using an Ar target. The detection of CE$\nu$NS has spawned a flurry of activities in high-energy physics, inspiring new constraints on beyond the Standard Model (BSM) physics, and new experimental methods. The CE$\nu$NS process has important implications for not only high-energy physics, but also astrophysics, nuclear physics, and beyond. This whitepaper discusses the scientific importance of CE$\nu$NS, highlighting how present experiments such as COHERENT are informing theory, and also how future experiments will provide a wealth of information across the aforementioned fields of physics., Comment: contribution to Snowmasss 2021. Contact authors: P. S. Barbeau, R. Strauss, L. E. Strigari

Zinc tungstate (ZnWO$_4$) crystal scintillators are promising detection material for the experiments searching for double beta decay, dark matter, and investigating rare alpha decays. An extended R&D was performed to develop advanced quality ZnWO$_4$ crystal scintillators. The R&D programme included the selection of the initial materials, the variation of the compound stoichiometry, the application of single and double crystallization, and the annealing of the crystal boules. The optical transmittance of the produced boules was measured, and the luminescence under X-ray excitation in the temperature region from 85 K to room temperature was studied (thermally stimulated luminescence was measured till 350 K). The energy resolution and the relative scintillation pulse amplitude were measured with gamma-sources demonstrating high scintillation properties of the samples produced by single crystallization from deeply purified zinc and tungsten oxides, with stoichiometric composition, annealed in air atmosphere., Comment: 14 pages; 10 figures

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., Comment: 44 pages, 20 figures; Editors: A. Fuss, M. Kaznacheeva, F. Reindl, F. Wagner; updated copyright statements and funding information

The NUCLEUS experiment aims to measure coherent elastic neutrino nucleus scattering of reactor anti-neutrinos using cryogenic calorimeters. Operating at an overburden of 3 m.w.e., muon-induced backgrounds are expected to be one of the dominant background contributions. Besides a high efficiency to identify muon events passing the experimental setup, the NUCLEUS muon veto has to fulfill tight spatial requirements to fit the constraints given by the experimental site and to minimize the induced detector dead-time. We developed highly efficient and compact muon veto modules based on plastic scintillators equipped with wavelength shifting fibers and silicon photo multipliers to collect and detect the scintillation light. In this paper, we present the full characterization of a prototype module with different light read-out configurations. We conclude that an efficient and compact muon veto system can be built for the NUCLEUS experiment from a cube assembly of the developed modules. Simulations show that an efficiency for muon identification of >99 % and an associated rate of 325 Hz is achievable, matching the requirements of the NUCLEUS experiment.

Experimental observations and theoretical arguments point out that Dark Matter (DM) particles are one of the most prominent component of the Universe. This motivated the pioneer DAMA experiment to investigate the presence of these particles in the galactic halo, by exploiting the model independent signature of the DM annual modulation of the rate and very highly radio-pure apparatus in underground site. In this paper the results obtained by other two annual cycles of DAMA/LIBRA-phase2 are presented and the long-standing model-independent annual modulation effect measured by DAMA deep underground at the Gran Sasso National Laboratory (LNGS) of the I.N.F.N. with different experimental configurations is summarized. The improved experimental configuration of DAMA/LIBRA-phase2, $\simeq$ 250 kg highly radio-pure NaI(Tl), allowed to lower the software energy threshold. The total exposure of DAMA/LIBRA-phase2 over 8 annual cycles is 1.53 ton $\times$ yr. DAMA/LIBRA-phase2 confirms the evidence of a signal that meets all the requirements of the model independent Dark Matter annual modulation signature, at 11.8 $\sigma$ C.L. in the energy region (1-6) keV. In the energy region between 2 and 6 keV, where data are also available from DAMA/NaI and DAMA/LIBRA-phase1 (2.86 ton $\times$ yr), the achieved C.L. is 13.7 $\sigma$; the modulation amplitude of the single-hit scintillation events is: $(0.01014 \pm 0.00074)$ cpd/kg/keV, the measured phase is $(142.4 \pm 4.2)$ days and the measured period is $(0.99834 \pm 0.00067)$ yr, all these values are well in agreement with those expected for DM particles. No systematics or side reaction able to mimic the exploited DM signature (i.e. to account for the whole measured modulation amplitude and to simultaneously satisfy all the requirements of the signature), has been found or suggested by anyone throughout some decades thus far., Comment: Proceedings of the Sixteenth Marcel Grossmann Meeting - MG16, July 5-10, 2021. arXiv admin note: substantial text overlap with arXiv:1805.10486, arXiv:1308.5109, arXiv:1002.1028, arXiv:1306.1411

The half-life of $^{212}$Po was measured with the highest up-to-date accuracy as $T_{1/2}=295.1(4)$ ns by using thorium-loaded liquid scintillator., Comment: 28 pages, 13 figures, 4 tables

Double-beta processes in $^{184}$Os and $^{192}$Os were searched for over 15851 h at the Gran Sasso National Laboratory (LNGS) of the I.N.F.N. by using a 118 g ultra-pure osmium sample installed on the endcap of a 112 cm$^3$ ultra-low-background broad-energy germanium detector. New limits on double-electron capture and electron capture with positron emission in $^{184}$Os were set at the level of $\lim T_{1/2} \sim 10^{16}-10^{17}$ yr. In particular the $2\nu$2K and $2\nu$KL decays of $^{184}$Os to the ground state of $^{184}$W are restricted as $T_{1/2}\geq3.0\times 10^{16}$ yr and $T_{1/2}\geq2.0\times 10^{16}$ yr, respectively. A lower limit on the half-life for the double-beta decay of $^{192}$Os to the first excited level of $^{192}$Pt was set as $\lim T_{1/2}=2.0\times 10^{20}$ yr at 90\% C.L., Comment: 22 pages, 9 figures, 2 tables

The development of low-threshold detectors for the study of coherent elastic neutrino-nucleus scattering and for the search for light dark matter necessitates methods of low-energy calibration. We suggest this can be provided by the nuclear recoils resulting from the $\gamma$ emission following thermal neutron capture. In particular, several MeV-scale single-$\gamma$ transitions induce well-defined nuclear recoil peaks in the 100 eV range. Using the FIFRELIN code, complete schemes of $\gamma$-cascades for various isotopes can be predicted with high accuracy to determine the continuous background of nuclear recoils below the calibration peaks. We present a comprehensive experimental concept for the calibration of CaWO$_4$ and Ge cryogenic detectors at a research reactor. For CaWO$_4$ the simulations show that two nuclear recoil peaks at 112.5 eV and 160.3 eV should be visible above background simply in the spectrum of the cryogenic detector. Then we discuss how the additional tagging for the associated $\gamma$ increases the sensitivity of the method and extends its application to a wider energy range and to Ge cryogenic detectors., Comment: 21 pages, 8 figures

Studies on double beta decay processes in $^{106}$Cd were performed by using a cadmium tungstate scintillator enriched in $^{106}$Cd at 66% ($^{106}$CdWO$_4$) with two CdWO$_4$ scintillation counters (with natural Cd composition). No effect was observed in the data accumulated over 26033 h. New improved half-life limits were set on the different channels and modes of the $^{106}$Cd double beta decay at level of $\lim T_{1/2}\sim 10^{20}-10^{22}$ yr. The limit for the two neutrino electron capture with positron emission in $^{106}$Cd to the ground state of $^{106}$Pd, $T^{2\nu\mathrm{EC}\beta^+}_{1/2}\geq2.1\times 10^{21}$ yr, was set by the analysis of the $^{106}$CdWO$_4$ data in coincidence with the energy release 511 keV in both CdWO$_4$ counters. The sensitivity approaches the theoretical predictions for the decay half-life that are in the range $T_{1/2}\sim10^{21}-10^{22}$ yr. The resonant neutrinoless double-electron capture to the 2718 keV excited state of $^{106}$Pd is restricted at the level of $T^{0\nu\mathrm{2K}}_{1/2}\geq2.9\times10^{21}$ yr, Comment: 16 pages, 10 figures, 2 tables

A search for $\alpha$ decay of naturally occurring osmium isotopes to the lowest excited levels of daughter nuclei has been performed by using an ultra-low-background Broad-Energy Germanium $\gamma$-detector with a volume of 112 cm$^3$ and an ultra-pure osmium sample with a mass of 118 g at the Gran Sasso National Laboratory of the INFN (Italy). The isotopic composition of the osmium sample has been measured with high precision using Negative Thermal Ionisation Mass Spectrometry. After 15851 h of data taking with the $\gamma$-detector no effect has been detected, and lower limits on the $\alpha$ decays were set at level of $\lim T_{1/2}\sim 10^{15}-10^{19}$ yr. The limits for the $\alpha$ decays of $^{184}$Os and $^{186}$Os to the first excited levels of daughter nuclei, $T_{1/2}(^{184}$Os$)\geq 6.8\times10^{15}$ yr and $T_{1/2}(^{186}$Os$)\geq3.3\times10^{17}$ yr (at 90% C.L.), exceed the present theoretical estimates of the decays half-lives. For $^{189}$Os and $^{192}$Os also decays to the ground states of the daughter nuclei were searched for due to the instability of the daughter nuclides relative to $\beta$ decay., Comment: 19 pages, 6 figures, 5 tables

Residual radioactive contaminants of a caesium hafnium chloride (Cs$_2$HfCl$_6$) crystal scintillator have been measured in a low background setup at the Gran Sasso National Laboratory of the INFN, Italy. The total alpha activity of the detector is at the level of 7.8(3) mBq/kg. The results of direct studies of the $\alpha$ decay of naturally occurring Hf isotopes that have been performed using the "source=detector" approach are presented. In 2848 h of data taking, the $\alpha$ decay of $^{174}$Hf was observed with T$_{1/2} = (7.0\pm1.2)\times10^{16} $ y., Comment: Accepted for publication in Nuclear Physics, Section A

The ZnWO$_4$ is an anisotropic crystal scintillator; for its peculiar characteristics, it is a very promising detector to exploit the so-called directionality approach in the investigation of those Dark Matter (DM) candidates inducing nuclear recoils. Recently, in the framework of the ADAMO project, an R\&D to develop high quality and ultra-radiopure ZnWO$_4$ crystal scintillators has been carried out. In the present paper the measurements to study the anisotropic response of a ZnWO$_4$ to $\alpha$ particles and to nuclear recoils induced by neutron scattering are reported. Monochromatic neutrons have been produced by a neutron generator at ENEA-CASACCIA. The quenching factor values for nuclear recoils along different crystallographic axes have been determined for three different nuclear recoils energies. These results open the possibility to realize a pioneer experiment to investigate the above mentioned DM candidates by means of the directionality., Comment: Proceedings of the IPRD 2019 Conference, 10 pages, 7 figures, accepted for publication in JINST

Anisotropic scintillators can offer a unique possibility to exploit the so-called directionality approach in order to investigate the presence of those Dark Matter (DM) candidates inducing nuclear recoils. In fact, their use can overcome the difficulty of detecting extremely short nuclear recoil traces. In this paper we present recent measurements performed on the anisotropic response of a ZnWO$_4$ crystal scintillator to nuclear recoils, in the framework of the ADAMO project. The anisotropic features of the ZnWO$_4$ crystal scintillators were initially measured with $\alpha$ particles; those results have been also confirmed by the additional measurements presented here. The experimental nuclear recoil data were obtained by using a neutron generator at ENEA-CASACCIA and neutron detectors to tag the scattered neutrons; in particular, the quenching factor values for nuclear recoils along different crystallographic axes have been determined for three different neutron scattering angles (i.e. nuclear recoils energies). From these measurements, the anisotropy of the light response for nuclear recoils in the ZnWO$_4$ crystal scintillator has been determined at 5.4 standard deviations., Comment: 22 pages; 12 figures. In press on Eur. Phys. J. A

The first direct search for the double electron capture ($2\epsilon$) and the electron capture with positron emission ($\epsilon\beta^+$) in $^{144}$Sm to the ground state and to the excited levels of $^{144}$Nd was realized by measuring - over 1899 h - a 342 g sample of highly purified samarium oxide (Sm$_2$O$_3$) with the ultra-low background HP-Ge $\gamma$ spectrometer GeCris (465 cm$^3$) at the STELLA facility of the Gran Sasso National Laboratory (LNGS). No effect was observed and half-life limits were estimated at the level of $T_{1/2} \sim (0.1-1.3) \times 10^{20}$ yr (90% C.L.). Moreover, for the first time half-life limits of the double beta ($2\beta^-$) decay of $^{154}$Sm to several excited levels of $^{154}$Gd have been set; they are at the level of $T_{1/2} \sim (0.06-8) \times 10^{20}$ yr (90% C.L.)., Comment: 20 pages, 7 figures and 4 tables

Several of the many proposed Dark Matter candidate particles, already investigated with lower exposure and a higher software energy threshold, are further analyzed including the first DAMA/LIBRA--phase2 data release, with an exposure of 1.13 ton $\times$ yr and a lower software energy threshold (1 keV). The cumulative exposure above 2 keV considering also DAMA/NaI and DAMA/LIBRA--phase1 results is now 2.46 ton $\times$ yr. The analysis permits to constraint the parameters' space of the considered candidates restricting their values -- with respect to previous analyses -- thanks to the increase of the exposure and to the lower energy threshold., Comment: 48 pages, 33 figures; in press on Nucl. Phys. At. Energy (2019)

The double-electron capture and the electron capture with positron emission in $^{168}$Yb have been investigated for the first time at the STELLA facility of the Gran Sasso underground laboratory (Italy) measuring 371 g of highly purified ytterbium oxide placed on the end-cap of a 465 cm$^3$ ultra-low-background high purity Germanium detector (HPGe). No gamma associated to double beta processes in $^{168}$Yb have been observed after 2074 h of data taking. This has allowed setting the half-life limits on the level of $\lim T_{1/2}\sim$ $10^{14}-10^{18}$ yr at 90\% C.L. Particularly, a lower half-life limit on a possible resonant neutrinoless double-electron capture in $^{168}$Yb to the $(2)^-$ 1403.7 keV excited state of $^{168}$Er is set as $T_{1/2}\geq1.9\times 10^{18}$ yr at 90\% C.L. Half-life limits $T_{1/2}^{2\nu(0\nu)}\geq 4.5(4.3)\times10^{16}$ yr were set on the $2\nu(0\nu)2\beta^-$ decay of $^{176}$Yb to the $2^+$ 84.3 keV first excited level of $^{176}$Hf., Comment: 23 pages, 6 figures, 4 tables

Precise measurement of half-life of $^{212}$Po (one of the daughter nuclides in radioactive chain of $^{232}$Th) was realized by means of liquid scintillator based on toluene doped by complex of thorium and trioctylphosphine oxide with concentration of Th $\sim0.1$ mass %. Fast photomultiplier tube and high frequency oscilloscope were used to acquire the scintillation signals waveforms. The algorithms were developed to find pairs of $^{212}$Bi beta-decays and subsequent $^{212}$Po alpha-decays, to calculate time differences between the events in the pair, and to build $^{212}$Bi beta-decay and $^{212}$Po alpha-decay energy spectra. Preliminary the $^{212}$Po half-life is $T_{1/2} = (294.8 \pm 1.9)$ ns. The experiment is in progress aiming at reduction of the statistical and systematic uncertainties., Comment: 7 pages, in Ukrainian, 7 figures

The double-beta decay of $^{116}$Cd has been investigated with the help of radiopure enriched $^{116}$CdWO$_4$ crystal scintillators (mass of 1.162 kg) at the Gran Sasso underground laboratory. The half-life of $^{116}$Cd relatively to the $2\nu2\beta$ decay to the ground state of $^{116}$Sn was measured with the highest up-to-date accuracy as $T_{1/2}=(2.63^{+0.11}_{-0.12})\times10^{19}$ yr. A new improved limit on the 0$\nu$2$\beta$ decay of $^{116}$Cd to the ground state of $^{116}$Sn was set as $T_{1/2}\geq 2.2 \times 10^{23}$ yr at 90\% C.L., which is the most stringent known restriction for this isotope. It corresponds to the effective Majorana neutrino mass limit in the range $\langle m_\nu\rangle\le(1.0-1.7)$ eV, depending on the nuclear matrix elements used in the estimations. New improved half-life limits for the 0$\nu$2$\beta$ decay with majoron(s) emission, Lorentz-violating $2\nu2\beta$ decay and $2\beta$ transitions to excited states of $^{116}$Sn were set at the level of $T_{1/2}\geq 10^{20}-10^{22}$ yr. New limits for the hypothetical lepton-number violating parameters (right-handed currents admixtures in weak interaction, the effective majoron-neutrino coupling constants, R-parity violating parameter, Lorentz-violating parameter, heavy neutrino mass) were set., Comment: 30 pages, 17 figures and 7 tables

The double beta decay of $^{150}$Nd to the first excited 0$^+$ level of $^{150}$Sm ($E_{exc}$ = 740.5 keV) has been investigated with the help of the ultra-low-background setup consisting of four HP Ge (high-purity germanium) detectors (${\approx}$ 225 cm$^3$ volume each one) at the Gran Sasso underground laboratory of INFN (Italy). A highly purified 2.381-kg sample of neodymium oxide (Nd$_2$O$_3$) was used as a source of ${\gamma}$ quanta expected in the decays. Gamma quanta with energies 334.0 keV and 406.5 keV emitted after deexcitation of the $0_1^+$ 740.5 keV level of $^{150}$Sm are observed in the coincidence spectra accumulated over 16375 h. The half-life relatively to the two neutrino double beta decay $^{150}$Nd $\rightarrow$ $^{150}$Sm(0$_1^+$) is measured as $T_{1/2} = [4.7_{-1.9}^{+4.1}\text{(stat)} {\pm} 0.5\text{(syst)}] {\times} 10^{19} y$, in agreement with results of previous experiments., Comment: 13 pages, 7 figures and 2 tables

The first search for double electron capture ($2\varepsilon$) and electron capture with positron emission ($\varepsilon\beta^+$) of $^{162}$Er to the ground state and to several excited levels of $^{162}$Dy was realized with 326 g of highly purified erbium oxide. The sample was measured over 1934 h by the ultra-low background HP Ge $\gamma$ spectrometer GeCris (465 cm$^3$) at the Gran Sasso underground laboratory. No effect was observed, the half-life limits were estimated at the level of $\lim T_{1/2}\sim 10^{15}-10^{18}$ yr. A possible resonant $0\nu KL_1$ capture in $^{162}$Er to the $2^+$ 1782.7 keV excited state of $^{162}$Dy is restricted as $T_{1/2}\geq5.0\times 10^{17}$ yr at 90% C.L. A new improved half-life limit $T_{1/2}\geq4.1\times 10^{17}$ yr was set on the $2\beta^-$ decay of $^{170}$Er to the $2^+$ 84.3 keV first excited state of $^{170}$Yb., Comment: 23 pages, 6 figures and 4 tables

The first model independent results obtained by the DAMA/LIBRA-phase2 experiment are presented. The data have been collected over 6 annual cycles corresponding to a total exposure of 1.13 ton $\times$ yr, deep underground at the Gran Sasso National Laboratory (LNGS) of the I.N.F.N. The DAMA/LIBRA-phase2 apparatus, $\simeq$ 250 kg highly radio-pure NaI(Tl), profits from a second generation high quantum efficiency photomultipliers and of new electronics with respect to DAMA/LIBRA-phase1. The improved experimental configuration has also allowed to lower the software energy threshold. New data analysis strategies are presented. The DAMA/LIBRA-phase2 data confirm the evidence of a signal that meets all the requirements of the model independent Dark Matter (DM) annual modulation signature, at 9.5 $\sigma$ C.L. in the energy region (1-6) keV. In the energy region between 2 and 6 keV, where data are also available from DAMA/NaI and DAMA/LIBRA-phase1 (exposure $1.33$ ton $\times$ yr, collected over 14 annual cycles), the achieved C.L. for the full exposure (2.46 ton $\times$ yr) is 12.9 $\sigma$; the modulation amplitude of the single-hit scintillation events is: $(0.0103 \pm 0.0008)$ cpd/kg/keV, the measured phase is $(145 \pm 5)$ days and the measured period is $(0.999 \pm 0.001)$ yr, all these values are well in agreement with those expected for DM particles. No systematics or side reaction able to mimic the exploited DM signature (i.e. to account for the whole measured modulation amplitude and to simultaneously satisfy all the requirements of the signature), has been found or suggested by anyone throughout some decades thus far., Comment: 28 pages, 17 figures, 5 tables. In press on Journal Nucl. Phys. and Atomic Energy. arXiv admin note: substantial text overlap with arXiv:1308.5109, arXiv:1002.1028, arXiv:1306.1411

Double beta decay of $^{116}$Cd has been investigated with the help of radiopure enriched $^{116}$CdWO$_4$ crystal scintillators in the experiment Aurora. The half-life of $^{116}$Cd relatively to the 2$\nu$2$\beta$ decay of $^{116}$Cd to the ground level of $^{116}$Sn is measured with the highest up-to-date accuracy as $T_{1/2}$ = [2.69 $\pm$ 0.02 (stat.) $\pm$ 0.14 (syst.)] $\times$ 10$^{19}$ yr. A new improved limit on the 0$\nu$2$\beta$ decay of $^{116}$Cd to the ground state of $^{116}$Sn is set as $T_{1/2}\geq 2.4 \times 10^{23}$ yr at 90\% C.L., that corresponds to the effective Majorana neutrino mass limit in the range $\langle$$m_\nu$$\rangle$ $\le$ $(1.1-1.6)$ eV, depending on the nuclear matrix elements used in the estimations. New improved limits on other $2\beta$ processes in $^{116}$Cd (decays with majoron emission, transitions to excited levels of $^{116}$Sn) were set at the level of $T_{1/2}\geq 10^{21}-10^{22}$ yr., Comment: 4 pages, 2 figures

A search for double electron capture ($2\varepsilon$), electron capture with positron emission ($\varepsilon\beta^+$), and double positron emission $2\beta^+$) in $^{136}$Ce and $^{138}$Ce was realized with a 465 cm$^3$ ultra-low background HP Ge $\gamma$ spectrometer over 2299 h at the Gran Sasso underground laboratory. A 627 g sample of cerium oxide deeply purified by liquid-liquid extraction method was used as a source of $\gamma$ quanta expected in double $\beta$ decay of the cerium isotopes. New improved half-life limits were set on different modes and channels of double $\beta$ decay of $^{136}$Ce and $^{138}$Ce at the level of $T_{1/2}>10^{17}-10^{18}$ yr., Comment: 19 pages, 6 figures, 2 tables

The DAMA experiment using ultra low background NaI(Tl) crystal scintillators has measured an annual modulation effect in the keV region which satisfies all the peculiarities of an effect induced by Dark Matter particles. In this paper we analyze this annual modulation effect in terms of mirror Dark Matter, an exact duplicate of ordinary matter from parallel hidden sector, which chemical composition is dominated by mirror helium while it can also contain significant fractions of heavier elements as Carbon and Oxygen. Dark mirror atoms are considered to interact with the target nuclei in the detector via Rutherford-like scattering induced by kinetic mixing between mirror and ordinary photons, both being massless. In the present analysis we consider various possible scenarios for the mirror matter chemical composition. For all the scenarios, the relevant ranges for the kinetic mixing parameter have been obtained taking also into account various existing uncertainties in nuclear and particle physics quantities., Comment: 30 pages, 16 figures, 3 tables, version in publication on Eur. Phys. J. C

The DAMA/LIBRA experiment ($\sim$ 250 kg of highly radio-pure NaI(Tl)) is running deep underground at the Gran Sasso National Laboratory (LNGS) of the I.N.F.N. Here we briefly recall the results obtained in its first phase of measurements (DAMA/LIBRA--phase1, total exposure: 1.04 ton $\times$ yr). DAMA/LIBRA--phase1 and the former DAMA/NaI (cumulative exposure: $1.33$ ton $\times$ yr) give evidence at 9.3 $\sigma$ C.L. for the presence of DM particles in the galactic halo by exploiting the model-independent DM annual modulation signature. No systematic or side reaction able to mimic the exploited DM signature has been found or suggested by anyone over more than a decade. At present DAMA/LIBRA--phase2 is running with increased sensitivity., Comment: Proceedings to the 19th Workshop "What Comes Beyond the Standard Models", Bled, July 11. -- 19., 2016

As low as possible radioactive contamination of a detector plays a crucial role to improve sensitivity of a double beta decay experiment. The radioactive contamination of a sample of $^{116}$CdWO$_4$ crystal scintillator by thorium was reduced by a factor $\approx 10$, down to the level 0.01 mBq/kg ($^{228}$Th), by exploiting the recrystallization procedure. The total alpha activity of uranium and thorium daughters was reduced by a factor $\approx 3$, down to 1.6 mBq/kg. No change in the specific activity (the total $\alpha$ activity and $^{228}$Th) was observed in a sample of ZnWO$_4$ crystal produced by recrystallization after removing $\approx 0.4$ mm surface layer of the crystal., Comment: 14 pages, 5 figures and 2 tables

A radiopure cadmium tungstate crystal scintillator, enriched in $^{106}$Cd to 66%, with mass of 216 g ($^{106}$CdWO$_4$), was used to search for double beta decay processes in $^{106}$Cd in coincidence with four ultra-low background high purity germanium detectors in a single cryostat. New improved limits on the double beta processes in $^{106}$Cd have been set on the level of $10^{20}- 10^{21}$ yr after 13085 h of data taking. In particular, the half-life limit on the two neutrino electron capture with positron emission, $T_{1/2}^{2\nu\varepsilon\beta^+}\geq 1.1\times 10^{21}$ yr, has reached the region of theoretical predictions. With this half-life limit the effective nuclear matrix element for the $2\nu\varepsilon\beta^+$ decay is bounded as $M^{2\nu\varepsilon\beta^+}_{eff}\le 1.1$. The resonant neutrinoless double electron captures to the 2718 keV, 2741 keV and 2748 keV excited states of $^{106}$Pd are restricted at the level of $T_{1/2} \geq (8.5\times10^{20}-1.4\times10^{21}$) yr., Comment: 18 pages, 11 figures, 1 table

A radiopure cadmium tungstate crystal scintillator, enriched in 106-Cd to 66%, with mass of 216 g (106-CdWO4) was used in coincidence with four ultra-low background HPGe detectors contained in a single cryostat to search for double beta decay processes in 106-Cd. New improved half-life limits on the double beta processes in 106-Cd have been set on the level of 1e20-1e21 yr after 13085 h of data taking deep underground (3600 m w.e.) at the Gran Sasso National Laboratories of INFN (Italy). In particular, the limit on the two neutrino electron capture with positron emission T1/2 >1.1e21 yr, has reached the region of theoretical predictions. The resonant neutrinoless double electron captures to the 2718, 2741 and 2748 keV excited states of 106-Pd are restricted on the level of T1/2 > 8.5e20 - 1.4e21 yr., Comment: 5 pages, submitted to proceedings of the TAUP'2015 Conference

The Aurora experiment to investigate double beta decay of $^{116}$Cd with the help of 1.162 kg cadmium tungstate crystal scintillators enriched in $^{116}$Cd to 82\% is in progress at the Gran Sasso Underground Laboratory. The half-life of $^{116}$Cd relatively to the two neutrino double beta decay is measured with the highest up-to-date accuracy $T_{1/2}=(2.62\pm0.14)\times10^{19}$ yr. The sensitivity of the experiment to the neutrinoless double beta decay of $^{116}$Cd to the ground state of $^{116}$Sn is estimated as $T_{1/2} \geq 1.9\times10^{23}$ yr at 90\% CL, which corresponds to the effective Majorana neutrino mass limit $\langle m_{\nu}\rangle \leq (1.2-1.8)$ eV. New limits are obtained for the double beta decay of $^{116}$Cd to the excited levels of $^{116}$Sn, and for the neutrinoless double beta decay with emission of majorons., Comment: 5 pages, 3 figures, 1 table, submitted as proceedings of the TAUP 2015 conference

The long-standing model-independent annual modulation effect measured by DAMA Collaboration is examined in the context of asymmetric mirror dark matter, assuming that dark atoms interact with target nuclei in the detector via kinetic mixing between mirror and ordinary photons, both being massless. The relevant ranges for the kinetic mixing parameter are obtained taking into account various existing uncertainties in nuclear and particle physics quantities as well as characteristic density and velocity distributions of dark matter in different halo models., Comment: 27 pages, 5 figures, 2 tables; version in publication on Eur. Phys. J. C