Explore the vast range of titles available.

Experimental data are presented for the charge collection efficiency for near-electrode interactions in cryogenic germanium detectors, and analyzed in terms of a model involving a phonon wind-driven expansion of the electron-hole cloud generated at the site of energy deposition. Computer simulations reproduce to an excellent accuracy the collection depth profiles as obtained by experiment and their dependence on the collection field and the nature of the electrode. Electrode-dependent effects in particular are explained by differences in the phonon reflection properties at the interface of the Ge crystal and the electrode.

The sensitivities of light Dark matter particle searches with cryogenic detectors are mostly limited by large backgrounds of events that do not produce ionization signal. The CRYOSEL project develops a new technique, where this background in a germanium cryogenic detector is rejected by using the signals from a superconducting single electron device (SSED) sensor designed to detect the phonons emitted through the Neganov–Trofimov–Luke effect by the e - h + pairs as they drift in a nearby very high-field region. A tag on signals from this device should suppress the heat-only background. The measurement of the response to IR laser pulses of the first CRYOSEL prototype show the relevance of such sensor technology.

Random coincidences of events could be one of the main sources of background in the search for neutrino-less double-beta decay of 100 Mo with macro-bolometers, due to their modest time resolution. Scintillating bolometers as those based on Li 2 MoO 4 crystals and employed in the CROSS and CUPID experiments can eventually exploit the coincident fast signal detected in a light detector to reduce this background. However, the scintillation provides a modest signal-to-noise ratio, making difficult a pile-up pulse-shape recognition and rejection at timescales shorter than a few ms. Neganov–Trofimov–Luke assisted light detectors (NTL-LDs) offer the possibility to effectively increase the signal-to-noise ratio, preserving a fast time-response, and enhance the capability of pile-up rejection via pulse shape analysis. In this article we present: (a) an experimental work performed with a Li 2 MoO 4 scintillating bolometer, studied in the framework of the CROSS experiment, and utilizing a NTL-LD; (b) a simulation method to reproduce, synthetically, randomly coincident two-neutrino double-beta decay events; (c) a new analysis method based on a pulse-shape discrimination algorithm capable of providing high pile-up rejection efficiencies. We finally show how the NTL-LDs offer a balanced solution between performance and complexity to reach background index ∼ 10 - 4 counts/keV/kg/year with 280 g Li 2 MoO 4 ( 100 Mo enriched) bolometers at 3034 keV, the Q β β of the double-beta decay, and target the goal of a next generation experiment like CUPID.

A bstract Neutrinoless double-beta decay is a key process in particle physics. Its experimental investigation is the only viable method that can establish the Majorana nature of neutrinos, providing at the same time a sensitive inclusive test of lepton number violation. CROSS (Cryogenic Rare-event Observatory with Surface Sensitivity) aims at developing and testing a new bolometric technology to be applied to future large-scale experiments searching for neutrinoless double-beta decay of the promising nuclei 100 Mo and 130 Te. The limiting factor in large-scale bolometric searches for this rare process is the background induced by surface radioactive contamination, as shown by the results of the CUORE experiment. The basic concept of CROSS consists of rejecting this challenging background component by pulse-shape discrimination, assisted by a proper coating of the faces of the crystal containing the isotope of interest and serving as energy absorber of the bolometric detector. In this paper, we demonstrate that ultra-pure superconductive Al films deposited on the crystal surfaces act successfully as pulse-shape modifiers, both with fast and slow phonon sensors. Rejection factors higher than 99.9% of α surface radioactivity have been demonstrated in a series of prototypes based on crystals of Li 2 MoO 4 and TeO 2 . We have also shown that point-like energy depositions can be identified up to a distance of ∼ 1 mm from the coated surface. The present program envisions an intermediate experiment to be installed underground in the Canfranc laboratory (Spain) in a CROSS-dedicated facility. This experiment, comprising ∼ 3 × 10 25 nuclei of 100 Mo, will be a general test of the CROSS technology as well as a worldwide competitive search for neutrinoless double-beta decay, with sensitivity to the effective Majorana mass down to 70 meV in the most favorable conditions.

Highly forbidden β decays provide a sensitive test to nuclear models in a regime in which the decay goes through high spin-multipole states, similar to the neutrinoless double- β decay process. There are only 3 nuclei ( 50 V, 113 Cd, 115 In) which undergo a 4 th forbidden non-unique β decay. In this work, we compare the experimental 113 Cd spectrum to theoretical spectral shapes in the framework of the spectrum-shape method. We measured with high precision, with the lowest energy threshold and the best energy resolution ever, the β spectrum of 113 Cd embedded in a 0.43 kg CdWO 4 crystal, operated over 26 days as a bolometer at low temperature in the Canfranc underground laboratory (Spain). We performed a Bayesian fit of the experimental data to three nuclear models (IBFM-2, MQPM and NSM) allowing the reconstruction of the spectral shape as well as the half-life. The fit has two free parameters, one of which is the effective weak axial-vector coupling constant, g A eff , which resulted in g A eff between 1.0 and 1.2, compatible with a possible quenching. Based on the fit, we measured the half-life of the 113 Cd β decay including systematic uncertainties as 7 . 73 - 0.57 + 0.60 × 10 15 yr, in agreement with the previous experiments. These results represent a significant step towards a better understanding of low-energy nuclear processes.

The Ricochet reactor neutrino observatory is planned to be installed at Institut Laue–Langevin starting in mid-2022. The scientific goal of the Ricochet collaboration is to perform a low-energy and percentage precision CENNS measurement in order to explore exotic physics scenarios beyond the standard model. To that end, Ricochet will host two cryogenic detector arrays: the CryoCube (Ge target) and the Q-ARRAY (Zn target), both with unprecedented sensitivity to O (10) eV nuclear recoils. The CryoCube will be composed of 27 Ge crystals of 38 g instrumented with NTD-Ge thermal sensor as well as aluminum electrodes operated at 10 mK in order to measure both the ionization and the heat energies arising from a particle interaction. To be a competitive CENNS detector, the CryoCube array is designed with the following specifications: a low-energy threshold ( ∼ 50  eV), the ability to identify and reject with a high efficiency the overwhelming electromagnetic backgrounds (gamma, beta, and X-rays), and a sufficient payload ( ∼ 1  kg). After a brief introduction of the future Ricochet experiment and its CryoCube, the current works and first performance results on the optimization of the heat channel, and the electrode designs will be presented. We conclude with a preliminary estimation of the CryoCube sensitivity to the CENNS signal within Ricochet .

The aim of the SELENDIS project within the EDELWEISS collaboration is to observe single e - h + pairs in lightweight (3.3 g) cryogenic germanium bolometers with charge and phonon readout at biases up to ∼ 100  V. These devices are ideal to characterize in detail the mechanism of charge creation and collection in cryogenic germanium detectors. Electron–hole pairs are produced in the bulk of the detector either by the injection of pulsed IR laser or by neutron activation of germanium inducing the K , L and M lines from 71 Ge electron capture decays. Low-energy laser pulses are also used to probe the single e - h + pair sensitivity of Ge bolometers. Preliminary results are used to compare these two modes of charge creation, an important step toward a detailed characterization of Ge bolometers for their use in sub-MeV dark matter searches.

We report on the low-temperature study of thick YSi films that are of potential interest for applications in low-temperature thermometry. Thick amorphous Y x S i 1 - x films (300 to 600 Å) have been synthesized, and the temperature variation in their resistance is studied as a function of the stoichiometry of the alloy. These measurements show that Y x S i 1 - x can exist in various states: insulating, metallic and superconducting. We have determined a preliminary phase diagram for the 3D Y x S i 1 - x alloy. On the superconducting side, the Y 30 S i 70 film shows a sharp transition at about 1K. This superconducting compound therefore is a promising candidate for transition-edge sensors.

Neutrinoless double-beta ( 0 ν β β ) decay is a hypothetical rare nuclear transition ( T 1 / 2 > 10 25 – 10 26 year). Its observation would provide an important insight into the nature of neutrinos (Dirac or Majorana particle) demonstrating that the lepton number is not conserved. This decay can be investigated with bolometers embedding the double-beta decay isotope ( 76 Ge , 82 Se , 100 Mo , 116 Cd , 130 Te ...), which perform as low-temperature calorimeters (few tens of mK) detecting particle interactions via a small temperature rise read out by a dedicated thermometer. Cryogenic Rare-event Observatory with Surface Sensitivity (CROSS) aims at the development of bolometric detectors (based on Li 2 MoO 4 and TeO 2 crystals) capable of discriminating surface α and β interactions by exploiting superconducting properties of Al film deposited on the detector surface. We report in this paper the results of tests on prototypes performed at CSNSM (Orsay, France) that showed the capability of a-few- μ m -thick superconducting Al film deposited on crystal surface to discriminate surface α from bulk events, thus providing the detector with the required pulse shape discrimination capability. The CROSS technology would further improve the background suppression and simplify the detector construction (no auxiliary light detector is needed to reject alpha surface events) with a view to future competitive double-beta decay searches.

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.