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Characterization of the magnetic fields at different scales in the Universe is a new frontier for submillimeter astronomy. Polarimetric measurements between 50 and 500 µm are the golden path for this research. We develop, in the prospect of space observatories, all-silicon 50 mK bolometer arrays with polarimetric capabilities in the pixel. Here, we present the first results of the new detectors: performances of thermal sensors, optical absorption and polarimetry.

As part of the R2D2 (Rare Decays with Radial Detector) R &D, the use of a gas detector with a spherical or cylindrical cathode, equipped with a single anode and operating at high pressure, was studied for the search of rare phenomena such as neutrinoless double-beta decay. The presented measurements were obtained with a cylindrical detector, covering gas pressures ranging from 1 to 10 bar in argon and 1 to 6 bar in xenon, using both a point-like source of 210 Po (5.3 MeV α ) and a diffuse source of 222 Rn (5.5 MeV α ). Analysis and interpretation of the data were developed using the anodic current waveform. Similar detection performances were achieved with both gases, and comparable energy resolutions were measured with both sources. As long as the purity of the gas was sufficient, no significant degradation of the measured energy was observed by increasing the pressure. At the highest operating pressure, an energy resolution better than 1.5% full-width at half-maximum (FWHM) was obtained for both gaseous media, although optimal noise conditions were not reached.

Total decay energy spectrometry with cryogenic detectors is a promising technique for radionuclide analysis of α-emitting nuclides. The radioactive sample is embedded in the detector absorber, and the total decay energy for each disintegration is measured as a temperature elevation. We are developing this technique with metallic magnetic calorimeters (MMCs). The main condition of this technique is a detection efficiency close to unity. However, some α-emitting nuclides emit intense γ-rays that can partially escape from the absorber. So a feasibility study for several nuclides has been carried out based on Monte Carlo simulations of the detection efficiency and numerical calculations of the expected energy resolution to identify the radionuclides that can potentially be measured. Furthermore, an MMC prototype has been built and tested. The total decay energy spectrum of Po-210 was measured, and a FWHM energy resolution of 1.25 keV at 5.4 MeV was obtained and a Gaussian width at half maximum of 0.827 (5) keV. The baseline FWHM energy resolution is 207 eV, consistent with the resolution obtained on low-energy L X-rays in the same spectrum at 14 keV.

The EDELWEISS collaboration aims for direct detection of light dark matter using germanium cryogenic detectors with low threshold phonon sensor technologies and efficient charge readout designs. We describe here the development of Ge bolometers equipped with high impedance thermistors based on a Nb x Si 1−x TES alloy. High aspect ratio spiral designs allow the TES impedance to match with JFET or HEMT front-end amplifiers. We detail the behavior of the superconducting transition properties of these sensors and the detector optimization in terms of sensitivity to a-thermal phonons. We report preliminary results of a 200 g Ge detector that was calibrated using 71 Ge activation by neutrons at the LSM underground laboratory.

In dark matter WIMP searches the fundamental background is due to neutron flux. Thus shielding plays a crucial role in attenuating this flux and consequently in suppressing nuclear recoil background events. The transition from EDELWEISS-II to EDELWEISS-III with a total fiducial mass of 24 kg and improved background rejection has required the modification of the neutron shielding. In this paper we describe the design of this new neutron shielding and give an estimate of the expected neutron rate in comparison with the EDELWEISS-II experiment.

We report on a dark matter search for a Weakly Interacting Massive Particle (WIMP) in the mass range m χ ∈ [ 4 , 30 ] GeV / c 2 with the EDELWEISS-III experiment. A 2D profile likelihood analysis is performed on data from eight selected detectors with the lowest energy thresholds leading to a combined fiducial exposure of 496 kg-days. External backgrounds from γ - and β -radiation, recoils from 206 Pb and neutrons as well as detector intrinsic backgrounds were modelled from data outside the region of interest and constrained in the analysis. The basic data selection and most of the background models are the same as those used in a previously published analysis based on boosted decision trees (BDT) [ 1 ]. For the likelihood approach applied in the analysis presented here, a larger signal efficiency and a subtraction of the expected background lead to a higher sensitivity, especially for the lowest WIMP masses probed. No statistically significant signal was found and upper limits on the spin-independent WIMP-nucleon scattering cross section can be set with a hypothesis test based on the profile likelihood test statistics. The 90 % C.L. exclusion limit set for WIMPs with m χ = 4 GeV / c 2 is 1.6 × 10 - 39 cm 2 , which is an improvement of a factor of seven with respect to the BDT-based analysis. For WIMP masses above 15 GeV / c 2 the exclusion limits found with both analyses are in good agreement.

A bstract This article describes BabyIAXO, an intermediate experimental stage of the International Axion Observatory (IAXO), proposed to be sited at DESY. IAXO is a large-scale axion helioscope that will look for axions and axion-like particles (ALPs), produced in the Sun, with unprecedented sensitivity. BabyIAXO is conceived to test all IAXO subsystems (magnet, optics and detectors) at a relevant scale for the final system and thus serve as prototype for IAXO, but at the same time as a fully-fledged helioscope with relevant physics reach itself, and with potential for discovery. The BabyIAXO magnet will feature two 10 m long, 70 cm diameter bores, and will host two detection lines (optics and detector) of dimensions similar to the final ones foreseen for IAXO. BabyIAXO will detect or reject solar axions or ALPs with axion-photon couplings down to g aγ ∼ 1 . 5 × 10 − 11 GeV − 1 , and masses up to m a ∼ 0 . 25 eV. BabyIAXO will offer additional opportunities for axion research in view of IAXO, like the development of precision x-ray detectors to identify particular spectral features in the solar axion spectrum, and the implementation of radiofrequency-cavity-based axion dark matter setups.

The project LUMINEU is mainly aiming at the search for neutrinoless double-beta decay of the candidate nuclide 100 Mo using cryogenic ZnMoO 4 detectors with simultaneous heat and scintillation light detection for radioactive background rejection. It also includes some development for dark matter search using cryogenic Ge detectors with simultaneous heat and ionization detection for background rejection. For both cases, metallic magnetic calorimeters (MMCs) are studied among several thermometer types. In double-beta decay search, the intrinsically fast response of MMCs reading out the light detector may allow for a very fast signal rise time and help to reduce the potential background due to pile-up of two-neutrino double beta decay events. In dark matter search, MMCs reading out the heat channel may improve the energy resolution with respect to the standard NTD Ge thermistor readout and hence the sensitivity of the detectors for low-mass WIMPs.

CUPID-Mo is a bolometric experiment to search for neutrinoless double-beta decay ( 0 ν β β ) of 100 Mo . In this article, we detail the CUPID-Mo detector concept, assembly and installation in the Modane underground laboratory, providing results from the first datasets. The CUPID-Mo detector consists of an array of 20 100 Mo -enriched 0.2 kg Li 2 MoO 4 crystals operated as scintillating bolometers at ∼ 20 mK . The Li 2 MoO 4 crystals are complemented by 20 thin Ge optical bolometers to reject α events by the simultaneous detection of heat and scintillation light. We observe a good detector uniformity and an excellent energy resolution of 5.3 keV (6.5 keV) FWHM at 2615 keV, in calibration (physics) data. Light collection ensures the rejection of α particles at a level much higher than 99.9% – with equally high acceptance for γ / β events – in the region of interest for 100 Mo 0 ν β β . We present limits on the crystals’ radiopurity: ≤ 3 μ Bq/kg of 226 Ra and ≤ 2 μ Bq/kg of 232 Th . We discuss the science reach of CUPID-Mo, which can set the most stringent half-life limit on the 100 Mo 0 ν β β decay in half-a-year’s livetime. The achieved results show that CUPID-Mo is a successful demonstrator of the technology developed by the LUMINEU project and subsequently selected for the CUPID experiment, a proposed follow-up of CUORE, the currently running first tonne-scale bolometric 0 ν β β experiment.

Detectors fitted with interleaved collection electrodes offer a promising solution to the problem of surface event rejection in cryogenic Ge detectors for dark matter search. Detector design and modeling are discussed, based on computer simulations of the collection field and on pulse-shape analysis of the ionization signals. Test experiments with a prototype detector are presented in a companion paper by X. Defay et al. in this conference.