[en] The absolute scale of the neutrino mass eigenstates is one of the puzzles in modern particle physics and can be directly investigated using electroweak decays. In the context of the ECHO collaboration we are developing low temperature metallic magnetic calorimeters (MMCs) to be used with an internal ¹⁶³Ho source to measure its electron capture spectrum. MMCs are calorimetric particle detectors operated below 100 mK based on a paramagnetic temperature sensor, that convert the temperature rise due to the absorption of an energetic particle to a change of magnetization which is detected by a SQUID magnetometer. These detectors fulfill the requirements for cryogenic neutrino mass investigations, namely an energy resolution ΔE_FWHM below 2 eV and pulse formation times of τ<1μs. ΔE_FWHM=2.0 eV and τ=90 ns have been observed in micro-fabricated MMCs for soft X-ray detection. We outline the scientific goals and the contributions of the participating groups of the recently formed ECHO collaboration. We present results obtained with a first detector prototype using a Au absorber with ¹⁶³Ho ions implanted at ISOLDE(CERN). The achieved energy resolution of ΔE_FWHM=12 eV and rise times of τ=90 ns are very promising results and encourage further investigation. An energy resolution of ΔE_FWHM=12 eV and rise times of τ=90 ns were measured and show the encouraging outcome of this approach.

[en] We present low temperature micro-calorimeters based on a novel sensor concept, the Magnetic Penetration Thermometers (MPTs). The MPTs make use of the temperature dependence of the critical magnetic field and the penetration depth of a superconducting sensor. The superconducting sensor is inductively coupled to a superconducting pick-up coil which also provides a bias magnetic field. The flux in the pick-up coil depends on the position of the interface between normal and superconducting regions in the sensor which in turn is a steep function of temperature. The change of magnetic flux upon the absorption of a particle is read-out by low-noise high-bandwidth dc-SQUIDs. Similar to metallic magnetic calorimeters, MPTs operate in a wide range of temperature and without intrinsic bias power dissipation. We present the results of numerical simulations for the signal size and energy resolution for various superconducting films based on a simple thermo-dynamical model, as well as first experimental results.

[en] The EDELWEISS-III direct dark matter search experiment uses cryogenic HP-Ge detectors Fully covered with Inter-Digitized electrodes (FID). They are operated at low fields (< 1 V/cm), and as a consequence charge-carrier trapping significantly affects both the ionization and heat energy measurements. This paper describes an analytical model of the signals induced by trapped charges in FID detectors based on the Shockley-Ramo theorem. It is used to demonstrate that veto electrodes, initially designed for the sole purpose of surface event rejection, can be used to provide a sensitivity to the depth of the energy deposits, characterize the trapping in the crystals, perform heat and ionization energy corrections and improve the ionization baseline resolutions. These procedures are applied successfully to actual data.

[en] We present the results of measurements demonstrating the efficiency of the EDELWEISS-III array of cryogenic germanium detectors for direct dark matter searches. The experimental setup and the FID (Fully Inter-Digitized) detector array is described, as well as the efficiency of the double measurement of heat and ionization signals in background rejection. For the whole set of 24 FID detectors used for coincidence studies, the baseline resolutions for the fiducial ionization energy are mainly below 0.7 keV_ee (FHWM) whereas the baseline resolutions for heat energies are mainly below 1.5 keV_ee (FWHM). The response to nuclear recoils as well as the very good discrimination capability of the FID design has been measured with an AmBe source. The surface β- and α-decay rejection power of R_surf < 4 × 10⁻⁵ per α at 90% C.L. has been determined with a ²¹⁰Pb source, the rejection of bulk γ-ray events has been demonstrated using γ-calibrations with ¹³³Ba sources leading to a value of R _{γ −mis−fid} < 2.5 × 10⁻⁶ at 90% C.L.. The current levels of natural radioactivity measured in the detector array are shown as the rate of single γ background. The fiducial volume fraction of the FID detectors has been measured to a weighted average value of (74.6 ± 0.4)% using the cosmogenic activation of the ⁶⁵Zn and ^68,71Ge isotopes. The stability and uniformity of the detector response is also discussed. The achieved resolutions, thresholds and background levels of the upgraded EDELWEISS-III detectors in their setup are thus well suited to the direct search of WIMP dark matter over a large mass range.

[en] We report on a dark matter search for a Weakly Interacting Massive Particle (WIMP) in the mass range m_χ element of [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 "2"0"6Pb 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 x 10"-"3"9 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. (orig.)

[en] This paper reports on the development of a technology involving ¹⁰⁰Mo-enriched scintillating bolometers, compatible with the goals of CUPID, a proposed next-generation bolometric experiment to search for neutrinoless double-beta decay. Large mass (∝ 1 kg), high optical quality, radiopure ¹⁰⁰Mo-containing zinc and lithium molybdate crystals have been produced and used to develop high performance single detector modules based on 0.2-0.4 kg scintillating bolometers. In particular, the energy resolution of the lithium molybdate detectors near the Q-value of the double-beta transition of ¹⁰⁰Mo (3034 keV) is 4-6 keV FWHM. The rejection of the α-induced dominant background above 2.6 MeV is better than 8σ. Less than 10 μBq/kg activity of ²³²Th(²²⁸Th) and ²²⁶Ra in the crystals is ensured by boule recrystallization. The potential of ¹⁰⁰Mo-enriched scintillating bolometers to perform high sensitivity double-beta decay searches has been demonstrated with only 10 kg x d exposure: the two neutrino double-beta decay half-life of ¹⁰⁰Mo has been measured with the up-to-date highest accuracy as T_1/2 = [6.90 ± 0.15(stat.) ± 0.37(syst.)] x 10¹⁸ years. Both crystallization and detector technologies favor lithium molybdate, which has been selected for the ongoing construction of the CUPID-0/Mo demonstrator, containing several kg of ¹⁰⁰Mo. (orig.)