[en] RES-NOVA is a newly proposed experiment for detecting neutrinos from astrophysical sources, mainly Supernovae, using an array of cryogenic detectors made of PbWO${}_4$ crystals produced from archaeological Pb. This unconventional material, characterized by intrinsic high radiopurity, enables low-background levels in the region of interest for the neutrino detection via Coherent Elastic neutrino-Nucleus Scattering (CEνNS). This signal lies at the detector energy threshold, O(1 keV), and it is expected to be hidden by naturally occurring radioactive contaminants of the crystal absorber. Here, we present the results of a radiopurity assay on a 0.84 kg PbWO${}_4$ crystal produced from archaeological Pb operated as a cryogenic detector. The crystal internal radioactive contaminations are: ${}^{232}$Th <40 µBq/kg, ${}^{238}$U <30 µBq/kg, ${}^{226}$Ra 1.3 mBq/kg and ${}^{210}$Pb 22.5 mBq/kg. We also present a background projection for the final experiment and possible mitigation strategies for further background suppression. The achieved results demonstrate the feasibility of realizing this new class of detectors.

[en] The detection of VUV scintillation light in (liquid) argon (LAr) detectors commonly includes a reflector with a fluorescent coating, converting UV photons to visible light. The light yield of these detectors depends directly on the conversion efficiency. Several coating/reflector combinations were produced using VM2000, a specular reflecting multi-layer polymer, and Tetratex®, a diffuse reflecting PTFE fabric, as reflector foils. The light yield of these coatings was optimised and has been measured in a dedicated liquid argon setup built at the University of Zurich. It employs a small, 1.3 kg LAr cell viewed by a 3-inch, low radioactivity PMT of type R11065-10 from Hamamatsu. The cryogenic stability of these coatings was additionally studied. The optimum reflector/coating combination was found to be Tetratex® dip-coated with Tetraphenyl-butadiene with a thickness of 0.9 mg/cm"2, resulting in a 3.6 times higher light yield compared to uncoated VM2000. Its performance was stable in long-term measurements, performed up to 100 days in liquid argon. This coated reflector was also investigated concerning radioactive impurities and found to be suitable for current and upcoming low-background experiments. Therefore it is used for the liquid argon veto in Phase II of the GERDA neutrinoless double beta decay experiment

[en] Simultaneous measurement of phonon and light signatures is an effective way to reduce the backgrounds and increase the sensitivity of CUPID, a next-generation bolometric neutrinoless double-beta decay (0νββ) experiment. Light emission in tellurium dioxide (TeO₂) crystals, one of the candidate materials for CUPID, is dominated by faint Cherenkov radiation, and the high refractive index of TeO₂ complicates light collection. Positive identification of 0νββ events therefore requires high-sensitivity light detectors and careful optimization of light transport. A detailed microphysical understanding of the optical properties of TeO₂ crystals is essential for such optimization. We present a set of quantitative measurements of light production and transport in a cubic TeO₂ crystal, verified with a complete optical model and calibrated against a UVT acrylic standard. We measure the optical surface properties of the crystal, and set stringent limits on the amount of room-temperature scintillation in TeO₂ for β and α particles of 5.3 and 8 photons/MeV, respectively, at 90% confidence. The techniques described here can be used to optimize and verify the particle identification capabilities of CUPID.

[en] CRESST is one of the most prominent direct detection experiments for dark matter particles with sub-GeV/c${}^2$ mass. One of the advantages of the CRESST experiment is the possibility to include a large variety of nuclides in the target material used to probe dark matter interactions. In this work, we discuss in particular the interactions of dark matter particles with protons and neutrons of ${}^6$Li. This is now possible thanks to new calculations on nuclear matrix elements of this specific isotope of Li. To show the potential of using this particular nuclide for probing dark matter interactions, we used the data collected previously by a CRESST prototype based on LiAlO${}_2$ and operated in an above ground test-facility at Max-Planck-Institut für Physik in Munich, Germany. In particular, the inclusion of ${}^6$Li in the limit calculation drastically improves the result obtained for spin-dependent interactions with neutrons in the whole mass range. The improvement is significant, greater than two order of magnitude for dark matter masses below 1 GeV/c${}^2$, compared to the limit previously published with the same data.

[en] High Purity Germanium detectors are used in many applications, from nuclear and astro-particle physics, to homeland security or environment protection. Although quite standard configurations are often used, with cryostats, charge sensitive amplifiers and analog or digital acquisition systems all commercially available, it might be the case that a few specific applications, e.g. satellites, portable devices, cryogenic physics experiments, etc. also require the development of a few additional or complementary techniques. An interesting case is for sure GERDA, the Germanium Detector Array experiment, searching for neutrino-less double beta decay of "7"6Ge at the Gran Sasso National Laboratory of INFN - Italy. In GERDA the entire detector array, composed of semi-coaxial and BEGe naked crystals, is operated suspended inside a cryostat filled with liquid argon, that acts not only as cooling medium and but also as an active shield, thanks to its scintillation properties. These peculiar circumstances, together with the additional requirement of a very low radioactive background from all the materials adjacent to the detectors, clearly introduce significant constraints on the design of the Ge front-end readout electronics. All the Ge readout solutions developed within the framework of the GERDA collaboration, for both Phase I and Phase II, will be briefly reviewed, with their relative strength and weakness compared together and with respect to ideal Ge readout. Finally, the digital processing techniques developed by the GERDA collaboration for energy estimation of Ge detector signals will be recalled. (authors)

[en] CUORE—the Cryogenic Underground Observatory for Rare Events—is an experiment searching for the neutrinoless double-beta (0νββ) decay of ¹³⁰Te with an array of 988 TeO₂ crystals operated as bolometers at ∼10 mK in a large dilution refrigerator. With this detector, we aim for a ¹³⁰Te 0νββ decay half-life sensitivity of 9×10²⁵ y with 5 y of live time, and a background index of $\lesssim <!--\; ???\; -->$ 10⁻² counts/keV/kg/y. Making an effort to maintain radiopurity by minimizing the bolometers' exposure to radon gas during their installation in the cryostat, we perform all operations inside a dedicated cleanroom environment with a controlled radon-reduced atmosphere. In this paper, we discuss the design and performance of the CUORE Radon Abatement System and cleanroom, as well as a system to monitor the radon level in real time.

[en] The Gerda experiment, located at the Laboratori Nazionali del Gran Sasso (LNGS) of INFN in Italy, searches for the neutrinoless double beta (0 νββ ) decay of ⁷⁶Ge. Gerda Phase II is aiming to reach a sensitivity for the 0 νββ half life of 10²⁶ yr in ∼ 3 years of physics data taking with 100 kg·yr of exposure and a background index of ∼ 10⁻³ cts/(keV·kg·yr). After 6 months of acquisition a first data release with 10.8 kg·yr of exposure is performed, showing that the design background is achieved. In this work a study of the Phase II background spectrum, the main spectral structures and the background sources will be presented and discussed. (paper)

[en] The GERDA experiment at the Laboratori Nazionali del Gran Sasso (LNGS) searches for the neutrinoless double beta decay of "7"6Ge. In view of the GERDA Phase II data collection, four new "2"2"8Th radioactive sources for the calibration of the germanium detectors enriched in "7"6Ge have been produced with a new technique, leading to a reduced neutron emission rate from (α, n) reactions. The gamma activities of the sources were determined with a total uncertainty of ∼4% using an ultra-low background HPGe detector operated underground at LNGS. The neutron emission rate was determined using a low background LiI(Eu) detector and a "3He counter at LNGS. In both cases, the measured neutron activity is ∼10"−"6 n/(s⋅Bq), with a reduction of about one order of magnitude with respect to commercially available "2"2"8Th sources. Additionally, a specific leak test with a sensitivity to leaks down to ∼10 mBq was developed to investigate the tightness of the stainless steel capsules housing the sources after their use in cryogenic environment

[en] The GERDA (GERmanium Detector Array) is an experiment for the search of neutrinoless double beta decay (0νββ) in ⁷⁶Ge, located at Laboratori Nazionali del Gran Sasso of INFN (Italy). GERDA operates bare high purity germanium detectors submersed in liquid Argon (LAr). Phase II of data-taking started in Dec 2015 and is currently ongoing. In Phase II 35 kg of germanium detectors enriched in ⁷⁶Ge including thirty newly produced Broad Energy Germanium (BEGe) detectors is operating to reach an exposure of 100 kg·yr within about 3 years data taking. The design goal of Phase II is to reduce the background by one order of magnitude to get the sensitivity for $T_{1/2}^{0\mathrm{\nu <!--\; ??\; -->}}=O\left({10}^{26}\right)\mathrm{y}\mathrm{r}$. To achieve the necessary background reduction, the setup was complemented with LAr veto. Analysis of the background spectrum of Phase II demonstrates consistency with the background models. Furthermore ²²⁶Ra and ²³²Th contamination levels consistent with screening results. In the first Phase II data release we found no hint for a 0νββ decay signal and place a limit of this process $T_{1/2}^{0\mathrm{\nu <!--\; ??\; -->}}>5.3\cdot <!--\; ???\; -->{10}^{25}$ yr (90% C.L., sensitivity 4.0·10²⁵ yr). First results of GERDA Phase II will be presented. (paper)

[en] The observation of neutrinoless double beta decay would allow to shed light onto the particle nature of neutrinos. Gerda is aiming to perform a background-free search for this process using high purity germanium detectors enriched in ⁷⁶Ge operated in liquid argon. This goal relies on the application of active background suppression techniques. A low background light instrumentation has been installed for Phase II to detect events with coincident energy deposition in the nearby liquid argon. The intended background index of ∼10⁻³ cts/(keV·ky·yr) has been confirmed. (paper)