Search

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. [ABSTRACT FROM AUTHOR]

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 NbxSi1−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 71Ge activation by neutrons at the LSM underground laboratory. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The Q & U Bolometric Interferometer for Cosmology (QUBIC) is a cosmology experiment that aims to measure the B-mode polarization of the cosmic microwave background (CMB). Measurements of the primordial B-mode pattern of the CMB polarization are in fact among the most exciting goals in cosmology as it would allow testing of the inflationary paradigm. Many experiments are attempting to measure the B-modes, from the ground and the stratosphere, using imaging Stokes polarimeters. The QUBIC collaboration developed an innovative concept to measure CMB polarization using bolometric interferometry. This approach mixes the high sensitivity of bolometric detectors with the accurate control of systematics due to the interferometric layout of the instrument. We present the calibration results for the Technological Demonstrator, before its commissioning in the Argentinian observing site and preparation for first light. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Q & U Bolometric Interferometer for Cosmology (QUBIC) is an international ground-based experiment dedicated in the measurement of the polarized fluctuations of the Cosmic Microwave Background. It is based on bolometric interferometry, an original detection technique which combines the immunity to systematic effects of an interferometer with the sensitivity of low-temperature incoherent detectors. QUBIC will be deployed in Argentina, at the Alto Chorrillos mountain site near San Antonio de los Cobres, in the Salta Province. The QUBIC detection chain consists in 2048 NbSi transition edge sensors (TESs) cooled to 350 mK.The voltage-biased TESs are read out with time domain multiplexing based on Superconducting QUantum Interference Devices at 1 K and a novel SiGe application-specific integrated circuit at 60 K allowing to reach an unprecedented multiplexing factor equal to 128. The QUBIC experiment is currently being characterized in the laboratory with a reduced number of detectors before upgrading to the full instrument. I will present the last results of this characterization phase with a focus on the detectors and readout system. [ABSTRACT FROM AUTHOR]

QUBIC is a ground-based experiment aiming to measure the B-mode polarization of the cosmic microwave background. The developed instrument is an innovative two-frequency band bolometric interferometer that will operate at 300 mK with NbSi TES arrays. In this paper, we describe the fabrication process of the detectors. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Cadmium-116 is one of the favorable candidates for neutrinoless double-beta decay ( 0 ν β β ) searches from both theoretical and experimental points of view, in particular thanks to the high energy of the decay (2813.49 keV), the possibility of the industrial enrichment in 116 Cd and its use in the well-established production of cadmium tungstate crystal scintillators. In this work, we present low-temperature tests of two 0.6 kg 116 CdWO 4 crystals enriched in 116 Cd to 82 % as scintillating bolometers. These detectors were operated underground, with one at the Laboratoire Souterrain de Modane (LSM) in France and the second at the Laboratorio Subterraneo de Canfranc (LSC) in Spain. The two crystals are coupled to bolometric Ge light detectors in order to register the scintillation light. The double readout of heat and scintillation enables reduction in the background in the region of interest by discriminating between different populations of particles. The main goal of these tests is the study of the crystals' radiopurity and the detectors' performance. The achieved results are extremely promising, in particular, the detectors demonstrate a high energy resolution (11–16 keV FWHM at 2615 keV) and a high-efficiency discrimination of the alpha background ( ∼ 20 σ ). These results, achieved for the first time with large mass enriched 116 CdWO 4 crystals, demonstrate prospects of the bolometric technology for high-sensitivity searches of 116 Cd 0 ν β β decay. [ABSTRACT FROM AUTHOR]

The dry cryostat technology is based on pulse tube cryo-coolers and offers a good alternative to wet dilution cryostats. However, the main drawback is the production of vibrations induced by the pulse tube. These vibrations can be transmitted to the cryogenic detectors mounted in the cryostat and cause extra-noises dramatically affecting their performance. A solution to mitigate the impact of these vibrations is to mount the detectors on a suspended tower. For this purpose, vibrations in a dry cryostat were modeled and preliminary prototypes were investigated in the scope of R&D for the EDELWEISS-III experiment. [ABSTRACT FROM AUTHOR]

Random coincidences of nuclear events can be one of the main background sources in low-temperature calorimetric experiments looking for neutrinoless doublebeta decay, especially in those searches based on scintillating bolometers embedding the promising double-beta candidate 100 Mo, because of the relatively short half-life of the twoneutrino double-beta decay of this nucleus. We show in this work that randomly coinciding events of the two-neutrino double-beta decay of 100 Mo in enriched Li2100 MoO4 detectors can be effectively discriminated by pulse-shape analysis in the light channel if the scintillating bolometer is provided with a Neganov-Luke light detector, which can improve the signal-to-noise ratio by a large factor, assumed here at the level of~750 on the basis of preliminary experimental results obtained with these devices. The achieved pile-up rejection efficiency results in a very low contribution, of the order of ~6 × 10-5 counts/(keV·kg·y), to the background counting rate in the region of interest for a large volume (~90 cm³) Li2100 MoO4 detector. This background level is very encouraging in view of a possible use of the Li2100 MoO4 solution for a bolometric tonne-scale next-generation experiment as that proposed in the CUPID project. [ABSTRACT FROM AUTHOR]

As part of the Q&U Bolometric Interferometer for Cosmology instrument targeting the cosmic microwave background primordial B-modes, two kilo-pixel focal planes have been designed for a NEP of $$\sim $$ $$3 \times 10^{-17}$$ W $$\sqrt{\mathrm {Hz}}$$ adapted for ground-based observations. Those pixels are transition edge sensors (TESs) made of voltage-biased NbSi thin films with a critical temperature $$T_\mathrm{c}$$ $$\sim $$ 400 mK and TiV absorbing grids. The TESs are coupled to a time-domain multiplexed electronics based on superconducting quantum interference devices and an additional SiGe cryogenic integrated circuit which provides a second multiplexing stage. In this paper, we briefly discuss the instrumental context of a quarter of focal plane (a 256-TES sub-array). Then, we present its typical manufacturing process and first test results at cryogenic temperature. [ABSTRACT FROM AUTHOR]

The detectors of the direct dark matter search experiment EDELWEISS consist of high-purity germanium crystals operated at cryogenic temperatures ( $$\mathrm {{<}20\,mK}$$ ) and low electric fields ( $$\mathrm {{<}1\,V/cm}$$ ). The surface discrimination is based on the simultaneous measurement of the charge amplitudes on different sets of electrodes. As the rise time of a charge signal strongly depends on the location of an interaction in the crystal, a time-resolved measurement can also be used to identify surface interactions. This contribution presents the results of a study of the discrimination power of the rise time parameter from a hot carrier transport simulation in combination with time-resolved measurements using an EDELWEISS-type detector in a test cryostat at ground level. We show the setup for the time-resolved ionization signal read-out in the EDELWEISS-III experiment and first results from data taking in the underground laboratory of Modane. [ABSTRACT FROM AUTHOR]

Bolometric detectors are excellent devices for the investigation of neutrinoless double-beta decay ( $$0\nu \beta \beta $$ ). The observation of such decay would demonstrate the violation of lepton number, and at the same time, it would necessarily imply that neutrinos are Majorana particles. The sensitivity of cryogenic detectors based on TeO $$_2$$ is strongly limited by the $$\alpha $$ -background in the region of interest for the 0 $$\nu \beta \beta $$ of $$^{130}$$ Te. It has been demonstrated that particle identification in TeO $$_2$$ bolometers is possible, measuring the Cherenkov light produced by particle interactions. However, the discrimination efficiency is low, and an event-by-event identification with NTD-based light detectors has to be demonstrated. We will discuss the performance of a highly sensitive light detector exploiting the Neganov-Luke effect for signal amplification. The detector, being operated with NTD thermistor and coupled to a 750 g TeO $$_2$$ crystal, shows the ability for an event-by-event identification of electron/gamma and $$\alpha $$ particles. The obtained results demonstrate the possibility to enhance the sensitivity of TeO $$_2$$ -based 0 $$\nu \beta \beta $$ experiment to an unprecedented level. [ABSTRACT FROM AUTHOR]

As a part of an R&D program to improve the sensitivity of its detectors to low-mass ( $$<$$ 10 GeV) weakly interacting massive particles, the Edelweiss dark matter collaboration is developing cryogenic ionization-and-heat coplanar grid germanium detectors, operated in a high-bias mode where advantage is taken of the voltage-assisted amplification of the ionization signals for enhanced sensitivity to low-energy ( $$<$$ a few keV) interactions. First results of $$\upgamma $$ calibration experiments are presented for a 200 g prototype detector, capable of sustaining collection voltages up to 180 V with a corresponding gain of 60 in the heat measurement channel for electron recoil interactions. Event populations are analyzed based on ionization and heat data and on computer modeling of the detector signals, and a tentative interpretation of the results for the heat resolution is presented, involving athermal ballistic phonon losses in the device with consequent fluctuations in the thermometer response to the energy deposit of a particle. [ABSTRACT FROM AUTHOR]

A new set of experimental data is presented for the mean drift lengths and the drift velocities of hot electrons and holes as a function of the electric field in ultra-pure and in lightly doped (n- and p-type) germanium single crystals at mK temperatures. Measurements are made in the field range between $$\sim $$ 0.1 and 15 V/cm, typical for the operation of cryogenic germanium detectors for dark matter search. The analysis of the experimental data strongly suggests that the dominant trapping centers are the dopant species in the neutral state. [ABSTRACT FROM AUTHOR]

Space-charge build-up phenomena are investigated in germanium detectors for dark matter search, associated with the thermal emission of carriers by the H $$^{-}$$ -like, dopant-related A $$^{+ }$$ and D $$^{-}$$ shallow trap centers. Evidence for such processes follows from a combined study of the time evolution of the pattern of charge sharing between the different collection electrodes of the device, and of the kinetics of carrier emission by the A $$^{+ }$$ and D $$^{- }$$ centers. Implications for detector physics are discussed. [ABSTRACT FROM AUTHOR]

Ionization detectors, based on the drift and collection of charges in high purity Germanium crystals (HP-Ge), are commonly used for gamma and particle detection. In the field of very low temperature detectors, several major experiments, like EDELWEISS or CDMS, are using such devices combined with a simultaneous measurement of the detector heat pulses, to search for dark matter in the universe. The leakage current between the charge collecting electrodes of the detectors must be kept as low as possible to preserve performance in terms of high resolution and low threshold. We present results concerning the surface treatment of EDELWEISS HP-Ge crystals, aiming at the reduction of their leakage currents at temperatures below 4 K. Among the explored solutions, a post-process dry-etching using XeF $$_{2}$$ (xenon difluoride) gives very promising and reproducible results. The modification of the Ge surface by this treatment and its effect on the low temperature leakage currents are discussed. [ABSTRACT FROM AUTHOR]

We are studying the properties of Niobium Silicon amorphous alloys as a candidate material for the fabrication of highly sensitive kinetic inductance detectors (KID), optimized for very low optical loads. As in the case of other composite materials, the NbSi properties can be changed by varying the relative amounts of its components. Using a NbSi film with T $$_c $$ = 1 K we have been able to obtain the first NbSi resonators, observe an optical response and acquire a spectrum in the band 50-300 GHz. The data taken show that this material has very high kinetic inductance $$L_k$$ and normal state surface resistivity $$\rho _n$$ . These properties are ideal for the development of KID. More measurements are planned to further characterize the NbSi alloy and fully investigate its potential. [ABSTRACT FROM AUTHOR]

As shown by the Planck mission (Planck Collaboration. Astronomy and astrophysics. arXiv1303.5071P, ), background limited bolometers in a space environment are very sensitive to high energy particles. In order to not degrade their sensitivity, it is necessary to reduce this unwanted signal. To achieve this goal, a good understanding of the detector's thermal architecture is mandatory. To investigate this question, we used an $$\alpha $$ particle source in front of our niobium silicon (NbSi) alloy Transition edge sensors (TES). The number of time constants required to fit the data and the way these time constants behave as we change the bias power gave us a good insight on the TES thermal architecture. Indeed we expect a decrease of the detector time constant due to the electro-thermal feedback properties. We will first present some standard characterizations of NbSi TES using a simple thermal model and how they indicate the presence of multiple thermal decouplings. Then we will show the results of the $$\alpha $$ particles measurements and how we used them to build our thermal model for Complex Impedance fitting. All this work has been done for the QUBIC experiment, a B-modes instrument. [ABSTRACT FROM AUTHOR]

Ultra-low temperature sensors provide unprecedented performances in X-ray and far infrared astronomy by taking advantage of physical properties of matter close to absolute zero. CESAR is an FP7 funded project started in December 2010, that gathers six European laboratories around the development of high performances cryogenic electronics. The goal of the project is to provide far-IR, X-ray and magnetic sensors with signal-processing capabilities at the heart of the detectors. We present the major steps that constitute the CESAR work, and the main results achieved so far. [ABSTRACT FROM AUTHOR]

Precise measurements of the cosmic microwave background (CMB) is crucial to cosmology, since any proposed model of the Universe must account for the features of this radiation. E_cient very large bolometer arrays (>10,000 pixels) constitute an important challenge for CMB observations and are actually developed by many groups worldwide. We present here an explorative new bolometer design based on a structure that simplifies the fabrication process and exhibits high sensitivity. This innovative device replaces delicate membrane-based structures and eliminates the mediation of phonons: the incoming energy is directly captured and measured in the electron bath of an appropriate sensor and the thermal decoupling is achieved via the intrinsic electron-phonon decoupling of the sensor at very low temperature. Reported results come from a 204-pixel matrix of NbSi transition edge sensors with a meander structure fabricated on a 2-inch silicon wafer using electron-beam co-evaporation and standard lithography process. To validate the application to CMB measurements, we have realized an optical calibration of our sample in the focal plane of a dilution cryostat test bench. [ABSTRACT FROM AUTHOR]

Anisotropy effects in hot carrier transport have been investigated in germanium crystals at mK temperatures in the electric field range pertaining to the operation of the Edelweiss dark matter detectors. Comparative measurements have been made on n-type specimens of different impurity contents, both ultra-pure ( N− N<10 cm) and doped to 10 cm. At relatively high field intensities (≳5 V/cm), similar features of electron and hole transport are observed independent of the concentration of electrically active impurities. Differences appear at lower field (down to a fraction of a V/cm) with regard to electron straggling especially, dependent on crystal purity. These experiments demonstrate the importance on carrier transport of impurity scattering at low field, whereas phonon scattering becomes the dominant factor at higher field intensities. [ABSTRACT FROM AUTHOR]

We present a prototype scintillating bolometer for the search for neutrinoless double β decay of Mo, consisting of a single ≈5 g ZnMoO crystal operated aboveground in the 20-30 mK temperature range. The scintillation light is read out by two thin Ge bolometers. The phonon signals are collected by NTD Ge thermistors. The ZnMoO crystal was grown with an advanced method (low-thermal-gradient Czochralski technique) and after purification of molybdenum. The results are very encouraging: the intrinsic energy resolution of the heat channel is ≈800 eV FWHM, the α/ β rejection factor (crucial for background suppression) is better than 99.9% in the region of interest for double β decay (≈3 MeV), and the radiopurity of ZnMoO looks substantially improved with respect to previous devices. [ABSTRACT FROM AUTHOR]

The most limiting factor for experiments looking for rare events, such as neutrinoless double beta decay, is the radioactive background. We will describe an innovative technique for the discrimination of the surface background which combine the use of thin layers of superconducting aluminum, deposited on a crystal operated as a macro-bolometer and with a fast thermistor, such as a NbSi thin film acting as out-of-equilibrium phonon sensor. The working principle is based on the fact that particles which transfer energy into the Al film create quasi-particles that release heat to the crystal with a considerable delay, that may be in the millisecond range. It is thus clear that pulses acquired from a fast thermistor in the case of surface and bulk events should have different shapes, depending on the place of the initial energy release. Here we present preliminary results on a small TeO crystal equipped with NbSi films and an Al film with a thickness of 10 μm. We prove that we are able to identify alpha surface events by pulse shape analysis with a good separation between bulk and surface events. The possibility to extend this rejection technique to bolometers equipped with slow temperature sensors as neutron transmutation doped Ge thermistors is under study. [ABSTRACT FROM AUTHOR]

We present preliminary results on characterisation of voltage biased superconducting bolometers with an NbSi alloy sensor. I( V) curves as well as complex impedance and noise measurements are carried out in a dilution fridge with a pulse tube as a first stage cooler. SQUIDs polarization and addressing are controlled by a cold ASIC in which a SiGe amplifier has been implemented. First characterisations were done on full membrane bolometers and show a noise level of about $10^{-16}\ \mathrm{W}/\sqrt{\mathrm{Hz}}$. Those detectors are developed for the QUBIC experiment, a B-modes telescope that will be deployed in Antactica in 2013. [ABSTRACT FROM AUTHOR]