Search

International audience; NUCLEUS is an experiment conceived for the detection of thecoherent elastic neutrino nucleus scattering. The experiment will be carried out in the nuclear power plant of Chooz-B in France that provides an intense flux of anti-neutrinos.The aim of NUCLEUS is to perform a very precise measurement of the coherent elastic scattering below 100 eV by employing extremely sensitive cryogenic detectors based on CaWO$_4$ and Al$_2$O$_3$ target crystals.At present, the NUCLEUS apparatus is in commissioning phaseat the Underground Laboratory of the Technical University Munich, where - after its installation and the first measurement phase - the experiment will be fully tested. Thereafter the entire apparatus will be moved to the reactor site at Chooz.

Despite the multiple and convincing evidence of the existence of dark matter (DM) in our Universe, its detection is one of the most pressing questions in particle physics. As of today, there is no unambiguous hint which could clarify the particle nature of DM. For these reasons, a huge experimental effort is ongoing, trying to realize experiments which can probe the particle properties of DM. In particular, direct search experiments are trying to cover the largest possible mass range, from a few MeVs up to TeVs. Particularly suited for the sub-GeV mass region are detectors containing light nuclei, which are sensitive to the scattering of light DM candidates. Among them, we investigate a carbon-based absorber to explore DM masses down to the MeV region. Thanks to their cryogenic properties (high Debye temperature and long-lived phonon modes), carbon-based materials operated as low temperature calorimeters could reach an energy threshold in the eV range and would allow for the exploration of new parameters of the DM–nucleus cross section. Despite several proposals, the possibility of operating a carbon-based cryogenic detector is yet to be demonstrated. In this contribution, the preliminary results obtained with a diamond absorber operated with a TES temperature sensor will be reported. The potential of such a detector in the current landscape of DM searches will also be illustrated.

COSINUS (Cryogenic Observatory for SIgnatures seen in Next-generation Underground Searches) is an experiment employing cryogenic calorimeters, dedicated to direct dark matter search in underground laboratories. Its goal is to cross-check the annual modulation signal the DAMA collaboration has been detecting for about 20 years (Bernabei et al. in Nucl Part Phys Proc 303–305:74–79, 2018. 10.1016/j.nuclphysbps.2019.03.015) and which has been ruled out by other experiments in certain dark matter scenarios. COSINUS can provide a model-independent test by the use of the same target material (NaI), with the additional chance of discriminating $$\beta /\gamma$$ β / γ events from nuclear recoils on an event-by-event basis, by the application of a well-established temperature sensor technology developed within the CRESST collaboration. Each module is constituted by two detectors: the light detector, that is a silicon beaker equipped with a transition edge sensor (TES), and the phonon detector, a small cubic NaI crystal interfaced with a carrier of a harder material (e.g. $$\hbox {CdWO}_4$$ CdWO 4 ), also instrumented with a TES. This technology had so far never been applied to NaI crystals because of several well-known obstacles, and COSINUS is the first experiment which succeeded in operating NaI crystals as cryogenic calorimeters. Here, we present the COSINUS project, describe the achievements and the challenges of the COSINUS prototype development and discuss the status and the perspectives of this NaI-based cryogenic frontier.

The NUCLEUS experiment aims for the detection of coherent elastic neutrino-nucleus scattering at a nuclear power reactor with gram-scale, ultra-low-threshold cryogenic detectors. This technology leads to a miniaturization of neutrino detectors and allows to probe physics beyond the Standard Model of particle physics. A 0.5 g NUCLEUS prototype detector, operated above ground in 2017, reached an energy threshold for nuclear recoils of below 20 eV. This sensitivity is achieved with tungsten transition edge sensors which are operating at temperatures of 15 mK and are mainly sensitive to non-thermal phonons. These small recoil energies become accessible for the first time with this technology, which allows collecting large-statistics neutrino event samples with a moderate detector mass. A first-phase cryogenic detector array with a total mass of 10 g enables a 5-sigma observation of coherent scattering within several weeks. We identified a suitable experimental site at the Chooz Nuclear Power Plant and performed muon and neutron background measurements there. The operation of a NUCLEUS cryogenic detector array at such a site requires highly efficient background suppression. NUCLEUS plans to use an innovative technique consisting of separate cryogenic anticoincidence detectors against surface backgrounds and penetrating (gamma, neutron) radiation. We present first results from prototypes of these veto detectors and their operation in coincidence with a NUCLEUS target detector.

The current results of direct dark matter searches are controversial. The long-standing dark-matter claim from the DAMA/LIBRA collaboration is excluded by null-results of several other experiments. However, a comparison of the results by experiments with different detector materials introduces model dependencies. The R&D project COSINUS (Cryogenic Observatory for SIgnatures seen in Next-generation Underground Searches) aims to develop cryogenic detectors based on (hygroscopic) sodium iodide (NaI). If successful, such detectors could be used in future experiments to investigate the origin of the annual modulation signal seen by the NaI-based scintillation detectors of the DAMA/LIBRA experiment. COSINUS detectors should be able to simultaneously detect phonons and scintillation light produced by a particle interaction inside the NaI crystal. This technique allows for an active suppression of β/γ backgrounds as well as detailed studies of a large variety of dark-matter models predicting nuclear interactions. For such kind of studies only moderate exposures of ≲100kg-days are needed. In addition to the projected sensitivities of COSINUS detectors, we also show the result of first tests using (only mildly hygroscopic) caesium iodide (CsI) crystals as target material. For this measurement we achieved an energy threshold of ∼4.7 keV for nuclear recoils.

CRESST-II is a direct dark matter experiment that uses scintillating calorimeters to detect WIMP-induced nuclear scatter processes. Heat and light signals are read out with tungsten transition edge sensors (TESs) that are optimized toward their sensitivity to non-thermal phonons. The usage of superconducting thin film structures (e.g., aluminum) serving as phonon collectors to increase the collection area for this signal component is an approach to improve the sensitivity of the TES. The performance of the phonon collectors depends on the material properties and the quality achieved in the production process. We optimized the size of the phonon collectors for the given quality of CRESST-II light detectors. The diffusion lengths measured in this work are $$\mathcal {O}$$ (1 mm) and show a strong correlation to the Residual Resistivity Ratio of the respective films. First tests of CRESST-II light detectors with larger as well as thicker phonon collectors individually show improvements in the measured pulse height of 30 %.

An active discrimination of the dominant $\alpha$-background is the prerequisite for future neutrinoless double-beta decay experiments based on TeO$_{2}$ bolometers. We investigate such $\alpha$-particle rejection in cryogenic TeO$_{2}$ bolometers by the detection of Cherenkov light. For a setup consisting of a massive TeO$_{2}$ crystal (285 g) and a separate cryogenic light detector, both using transition edge sensors as temperature sensors operated at around 10 mK, we obtain an event-by-event identification of e/$\gamma$- and $\alpha$-events. We find in the energy interval ranging from 2400 keV to 2800 keV and covering the Q-value of the neutrinoless double-beta decay of $^{130}$Te a separation of the means of the two populations of 3.7 times their width., Comment: 8 pages, 7 figures

The CRESST-III experiment which is dedicated to low-mass dark matter search uses scintillating CaWO$_4$ crystals operated as cryogenic particle detectors. Background discrimination is achieved by exploiting the scintillating light signal of CaWO$_4$ and by a novel active detector holder presented in this paper. In a test setup above ground, a nuclear-recoil energy threshold of $E_{th}=(190.6\pm5.2)$eV is reached with a 24g prototype detector, which corresponds to an estimated threshold of $\sim$50eV when being operated in the low-noise CRESST cryostat. This is the lowest threshold reported for direct dark matter searches. For CRESST-III phase 1, ten such detector modules were installed in the cryostat which have the potential to improve significantly the sensitivity to scatterings of dark matter particles with masses down to $\sim$0.1GeV/c$^2$., 12 pages, 5 figures

The CRESST-III experiment (Cryogenic Rare Events Search with Superconducting Thermometers), located at the underground facility Laboratori Nazionali del Gran Sasso in Italy, uses scintillating CaWO $$_4$$ crystals as cryogenic calorimeters to search for direct dark matter interactions in detectors. A large part of the parameter space for spin-independent scattering off nuclei remains untested for dark matter particles with masses below a few GeV/c $$^2$$ , despite many naturally motivated theoretical models for light dark matter particles. The CRESST-III detectors are designed to achieve the performance required to probe the low-mass region of the parameter space with a sensitivity never reached before. In this paper, new results on the performance and an overview of the CRESST-III detectors will be presented, emphasizing the results about the low-energy threshold for nuclear recoil of CRESST-III Phase 1 which started collecting data in August 2016.

The Cryogenic Observatory for SIgnals seen in Next-generation Underground Searches (COSINUS) project aims to provide a model-independent cross-check of the long-standing DAMA/LIBRA claim on the observation of dark matter by using the same target material, but in a different experimental approach. Operating sodium iodide (NaI) scintillating crystals as low-temperature scintillating calorimeters has the distinct advantage of providing a lower energy threshold for nuclear recoil events as expected from dark matter particle interactions combined with particle discrimination. The dual readout of phonon and light allows us to provide background rejection on an event-by-event basis, a unique feature in comparison with other NaI-based dark matter searches. The manuscript discusses in detail the COSINUS detector concept and presents the results and performance parameters from our second prototype detector.

The CRESST experiment uses cryogenic detectors based on transition-edge sensors to search for dark matter interactions. Each detector module consists of a scintillating CaWO $$_4$$ crystal and a silicon-on-sapphire (SOS) light detector which operate in coincidence (phonon-light technique). The 40-mm-diameter SOS disks (2 g mass) used in the data taking campaign of CRESST-II Phase 2 (2014–2016) reached absolute baseline resolutions of $$\sigma =$$ 4–7 eV. This is the best performance reported for cryogenic light detectors of this size. Newly developed silicon beaker light detectors (4 cm height, 4 cm diameter, 6 g mass), which cover a large fraction of the target crystal surface, have achieved a baseline resolution of $$\sigma = 5.8\,$$ eV. First results of further improved light detectors developed for the ongoing low-threshold CRESST-III experiment are presented.

We discuss a small-scale experiment, called $\nu$-cleus, for the first detection of coherent neutrino-nucleus scattering by probing nuclear-recoil energies down to the 10 eV-regime. The detector consists of low-threshold CaWO$_4$ and Al$_2$O$_3$ calorimeter arrays with a total mass of about 10 g and several cryogenic veto detectors operated at millikelvin temperatures. Realizing a fiducial volume and a multi-element target, the detector enables active discrimination of $\gamma$, neutron and surface backgrounds. A first prototype Al$_2$O$_3$ device, operated above ground in a setup without shielding, has achieved an energy threshold of ${\sim20}$ eV and further improvements are in reach. A sensitivity study for the detection of coherent neutrino scattering at nuclear power plants shows a unique discovery potential (5$\sigma$) within a measuring time of ${\lesssim2}$ weeks. Furthermore, a site at a thermal research reactor and the use of a radioactive neutrino source are investigated. With this technology, real-time monitoring of nuclear power plants is feasible.

The energy threshold of a cryogenic calorimeter can be lowered by reducing its size. This is of importance since the resulting increase in signal rate enables new approaches in rare-event searches, including the detection of MeV mass dark matter and coherent scattering of reactor or solar neutrinos. A scaling law for energy threshold vs. detector size is given. We analyze the possibility of lowering the threshold of a gram-scale cryogenic calorimeter to the few eV regime. A prototype 0.5 g Al$_2$O$_3$ device achieved an energy threshold of (${19.7\pm0.1}$) eV, the lowest value reported for a macroscopic calorimeter., 7 pages, 8 figures

Solid state detectors and low-temperature calorimeters are widely employed in rare event searches, because of their excellent sensitivity and consequent low energy threshold. A common procedure to establish the energy threshold is to define the trigger level at a fixed number of baseline standard deviations (sigmas) above the baseline level, typically 3 σ or 5 σ . This is not an ideal option when the threshold becomes a critical parameter for the detectors, requiring an optimised definition of the trigger. Recorded events with a small amplitude-to-noise ratio likely survive the selection criteria of the analysis chain contributing to the experiment background. We present a method to quantify the lowest trigger threshold achievable as a function of the acceptable amount of noise events triggered for the physics case under investigation. We then apply this novel method to existing experimental and simulated data to validate the model we presented.

The CRESST-III experiment, located in the Gran Sasso underground laboratory (LNGS, Italy), aims at the direct detection of dark matter (DM) particles. Scintillating CaWO(4) crystals operated as cryogenic detectors are used as target material for DM-nucleus scattering. The simultaneous measurement of the phonon signal from the CaWO(4) crystal and of the emitted scintillation light in a separate cryogenic light detector is used to discriminate backgrounds from a possible dark matter signal. The experiment aims to significantly improve the sensitivity for low-mass (≲ 5-10 GeV/c(2)) DM particles by using optimized detector modules with a nuclear recoil-energy threshold ≲ 100 eV. The current status of the experiment as well as projections of the sensitivity for spin-independent DM-nucleon scattering will be presented.

The next generation direct dark matter experiment CRESST-III has a high potential to significantly increase the sensitivity to low-mass WIMPs (mx ≲10 GeV/c2). We present the new CRESST detector module: it consists of a 24 g CaWO4 crystal operated as a phonon detector and a 20x20 mm^2 silicon-on-sapphire light detector. The phonon energy threshold is lowered to ~100 eV and a light detector resolution of typically 5 eV is achieved. A fully-scintillating inner detector housing is realised which efficiently rejects events from surface alpha decays. The CaWO4 sticks holding the target crystal are also operated as calorimeters to discriminate all possible artefacts related to the support structure. A projection for the sensitivity to spin-independent WIMP-nucleon scattering is given for the first phase of CRESSTIII which will start beginning of 2016.

The CRESST experiment in its first phase is using sapphire detectors with tungsten phase transition thermometers to search for dark matter WIMPs. At present Four 262 g detectors are performing first measurements under low background conditions. Detector performance as well as preliminary results from the background runs are presented. A second phase of CRESST using CaWO4 and simultaneous measurement of phonons and scintillation light is in preparation. (C) 2000 Elsevier Science B.V. All rights reserved.

International audience; EURECA (European Underground Rare Event Calorimeter Array) is a new project, searching for dark matter, with largely the present groups of the CRESST and EDELWEISS experiments and already a few new groups. The aim is to explore scalar cross sections in the 10−9–10−10 picobarn region with a target mass of up to one tonne. A major advantage of EURECA is our planned use of more that just one target material (multi target experiment for WIMP identification). In preparation for this large-scale experiment, R&D for EURECA is provided through the current phases of CRESST and EDELWEISS.

The CRESST cryogenic direct dark matter search at Gran Sasso, searching for WIMPs via nuclear recoil, has been upgraded to CRESST-II by several changes and improvements.We present the results of a commissioning run carried out in 2007. The basic element of CRESST-II is a detector module consisting of a large (~ 300 g) CaWO_4 crystal and a very sensitive smaller (~ 2 g) light detector to detect the scintillation light from the CaWO_4.Information from light-quenching factor studies allows the definition of a region of the energy-light yield plane which corresponds to tungsten recoils. A neutron test is reported which supports the principle of using the light yield to identify the recoiling nucleus. Data obtained with two detector modules for a total exposure of 48 kg-days are presented. Judging by the rate of events in the "all nuclear recoils" acceptance region the apparatus shows a factor ~ten improvement with respect to previous results, which we attribute principally to the presence of the neutron shield. In the "tungsten recoils" acceptance region three events are found, corresponding to a rate of 0.063 per kg-day. Standard assumptions on the dark matter flux, coherent or spin independent interactions,then yield a limit for WIMP-nucleon scattering of 4.8 \times 10^{-7}pb, at M{WIMP} ~50 GeV., Comment: 10 pages, 9 figs No essential changes in content. Minor errors corrected. Sentence added at end of introduction concerning increased sensitivity. Best limit on plots at M=50 GeV. Text labelling of candidate events corrected

An important aspect of dark matter search experiments is the active background reduction by identification of the type of particle interacting in the detector. In CRESST this is achieved by a simultaneous detection of heat and light produced by an interaction in a scintillating crystal. The overall light collection efficiency is a crucial parameter in order to achieve enough sensitivity to measure the small fraction of the deposited energy that is emitted as scintillation light. For this purpose, a thin superconducting lead film deposited on sapphire substrates has been tested as an alternative light absorber to a silicon absorber. The first results already show a better light absorption of the lead film. Other superconducting films are also being analyzed.

The R&D project COSINUS (Cryogenic Observatory for SIgnatures seen in Next-generation Underground Searches) aims to develop a cryogenic scintillating calorimeter using NaI as target crystal for direct darkmatter search. Dark matter particles interacting with the detector material generate both a phonon signal and scintillation light. While the phonon signal provides a precise determination of the deposited energy, the simultaneously measured scintillation light allows for a particle identification on an event-by-event basis, a powerful tool to study material-dependent interactions, and to suppress backgrounds. Using the same target material as the DAMA/LIBRA collaboration, the COSINUS technique may offer a unique possibility to investigate and contribute information to the presently controversial situation in the dark matter sector. We report on the dedicated design planned for the NaI proof-of-principle detector and the objectives of using this detection technique in the light of direct dark matter detection., 6 pages, 3 figures

Cryogenic detectors have a long history of success in the field of rare event searches. In particular scintillating calorimeters are very suitable detectors for this task since they provide particle discrimination: the simultaneous detection of the thermal and the light signal produced by a particle interaction in scintillating crystals allows to identify the nature of particle, as the light yield depends thereon. We investigate the performance of two large CsI (undoped) crystals ($\sim$122 g each) operated as scintillating calorimeters at milli-Kelvin temperatures in terms of calorimetric properties and background rejection capabilities. Furthermore, we discuss the feasibility of this detection approach towards a background-free future dark matter experiment based on alkali halides crystals, with active particle discrimination via the two-channel detection., Comment: 9 pages, 6 figures

The cryogenic dark matter experiment CRESST-II aims at the direct detection of WIMPs via elastic scattering off nuclei in scintillating CaWO$_4$ crystals. We present a new, highly improved, detector design installed in the current run of CRESST-II Phase 2 with an efficient active rejection of surface-alpha backgrounds. Using CaWO$_4$ sticks instead of metal clamps to hold the target crystal, a detector housing with fully-scintillating inner surface could be realized. The presented detector (TUM40) provides an excellent threshold of ${\sim}\,0.60\,$keV and a resolution of $\sigma\,{\approx}\,0.090$ keV (at 2.60$\,$keV). With significantly reduced background levels, TUM40 sets stringent limits on the spin-independent WIMP-nucleon scattering cross section and probes a new region of parameter space for WIMP masses below 3$\,$GeV/c$^2$. In this paper, we discuss the novel detector design and the surface-alpha event rejection in detail., Comment: 9 pages, 6 figures

The CRESST Phase II experiment at Gran Sasso is using 300 g scintillating CaWO4 crystals as absorbers for direct WIMP (weakly interactive massive particles) detection. The phonon signal in the CaWO4 crystal is registered in coincidence with the light signal, which is measured with a separate cryogenic light detector. The absorber crystal and the silicon light detector are read out by tungsten superconducting phase transition thermometers (W-SPTs). As a result an active discrimination of the electron recoils against nuclear recoils is achieved. Results on the properties of the detector modules and on the WIMP sensitivity are presented. (C) 2005 Published by Elsevier B.V.

We present first significant limits on WIMP dark matter by the phonon-light technique, where combined phonon and light signals from a scintillating cryogenic detector are used. Data from early 2004 with two 300 g CRESST-II prototype detector modules are presented, with a net exposure of 20.5 kg days. The modules consist of a CaWO4 scintillating ``target'' crystal and a smaller cryogenic light detector. The combination of phonon and light signals leads to a strong suppression of non-nuclear recoil backgrounds. Using this information to define an acceptance region for nuclear recoils we have 16 events from the two modules, corresponding to a rate for nuclear recoils between 12 and 40 keV of (0.87 +- 0.22) events/(kg day). This is compatible with the rate expected from neutron background, and most of these events lie in the region of the phonon-light plane anticipated for neutron-induced recoils. A particularly strong limit for WIMPs with coherent scattering results from selecting a region of the phonon-light plane corresponding to tungsten recoils, where the best module shows zero events., Comment: 24 pages, 10 figures, version v2 includes figures with improved print quality, v3 accepted for publication in astroparticle physics

CRESST-II detector modules rely on the ability to actively discriminate electron recoils from nuclear recoils via simultaneous measurement of phonons and scintillation light. The scintillation light produced in each target crystal is detected via an associated calorimeter consisting of a thin silicon wafer read out by a tungsten phase transition thermometer deposited on its surface. About 1% of the energy deposited in CaWO4 is detected as scintillation light; therefore, the sensitivity of the light detector is crucial for the discrimination of electron recoils from nuclear recoils at energies relevant for WIMP searches. We report the detector performance obtained using a thermometer geometry characterized by phonon collectors and a thin film thermal coupling to the heat sink (Fig. 1). This concept allows a high sensitivity by decoupling the area required for the collection of non-thermal phonons and the heat capacity of the sensor. With a 30×30×0.45 mm3 light detector, energy thresholds below 5 keV referred to energy deposition in CaWO4 have been obtained. Results achieved will be presented and an overview on further possibilities of development will be given.

The CRESST experiment (Cryogenic Rare Event Search with Superconducting Thermometers) searches for dark matter via the phonon and light signals of elastic scattering processes in scintillating crystals. The discrimination between a possible dark matter signal and background is based on the light yield. We present a new method for evaluating the two characteristics of a phonon/light detector module that determine how much of the deposited energy is converted to scintillation light and how efficiently a module detects the produced light. In contrast to former approaches with dedicated setups, we developed a method which allows us to use data taken with the cryogenic setup, during a dark matter search phase. In this way, we accounted for the entire process that occurs in a detector module, and obtained information on the light emission of the crystal as well as information on the performance of the module (light transport and detection). We found that with the detectors operated in CRESST-II phase 1, about 20% of the produced scintillation light is detected. A part of the light is likely absorbed by creating meta-stable excitations in the scintillating crystals. The light not detected is not absorbed entirely, as an additional light detector can help to increase the fraction of detected light.

We have developed massive cryogenic particle detectors to be used in the CRESST dark matter search. Each detector is made of a sapphire crystal and a tungsten superconducting phase transition thermometer. In this paper, we report on the results obtained with four 262 g detectors, which show energy thresholds as low as 350 eV and good energy resolution at low energies. The shape of the experimental pulses, the linearity of the detector response and the energy dependence of the resolution are discussed.

The current status of the direct Dark Matter experiments CRESST (Cryogenic Rare Event Search with Superconducting Thermometers) and the planned EURECA (European Underground Rare Event Calorimeter Array) is presented. Both experiments are aimed at the direct detection of WIMPs (Weakly Interacting Massive Particles), potential candidates for the Dark Matter in the universe. New design developments of the cryogenic detectors operated at mK temperatures are investigated to optimize detector performance and to simplify mass production. Thus, CRESST is also providing a basis for the EURECA project, aimed at a ton of cryogenic detectors with a multi-material target. © 2010 Elsevier B.V. All rights reserved.

We report on simultaneous detection of phonons and scintillation light using a cryogenic calorimeter composed of a scintillating CaWO 4 crystal and a separate light detector, both instrumented with a tungsten superconducting phase transition thermometer operating at about 12 mK. Clear discrimination between electron and nuclear recoils was demonstrated by irradiating the detector with electrons, photons and neutrons. The shape of the nuclear recoil energy spectrum induced by the neutrons could be well reproduced by simulations.

We are developing cryogenic detectors based on Ir/Au phase transition thermometers and superconducting aluminium tunnel junctions for different applications, where a high-energy resolution and a low detection threshold is required. These applications comprise low background experiments such as CRESST and GNO as well as high-energy resolution X-ray spectroscopy for astrophysics and fluorescence analysis where energy resolutions below 30 eV (FWHM) at 5.89 keV were achieved.

The CRESST experiment is set up in the Gran Sasso Underground Laboratory to search for hypothetical Weakly Interacting Massive Particles (WIMPs) with cryogenic detectors. It is expected that WIMPs can transfer a part of their energy (up to some tens of keV) via scattering off a nucleus of an absorber. In order to detect these small energies Superconducting Phase transition Thermometers (SPTs) are used at very low temperatures. In this article the principle of the SPTs is introduced. The techniques to produce SPTs with a reproducible transition temperature of 15±5 mK are shown.

We report on a newly developed detector based on a Superconducting-Phase-Transition Thermometer which is used in a Time-of-flight mass spectrometer for heavy molecules. It exhibits a sensitive area of 3.0×3.0 mm 2 and a time resolution of approximately 1.1 μs . First measurements with our setup on heavy proteins up to 150,000 amu are presented.

We report on the development of a SQUID read-out for a fast cryogenic detector with superconducting phase transition thermometer. To avoid the usual transformer matching and modulation–demodulation technique we are using a second SQUID to amplify the signal of a first stage input SQUID. A bandwidth of 2 MHz and a slew rate of 2×105 Φ0 s−1 were achieved. The system is developed for the detection of large protein molecules in a time of flight mass spectrometer.

The CRESST experiment monitors 300g CaWO_4 crystals as targets for particle interactions in an ultra low background environment. In this paper, we analyze the background spectra that are recorded by three detectors over many weeks of data taking. Understanding these spectra is mandatory if one wants to further reduce the background level, and allows us to cross-check the calibration of the detectors. We identify a variety of sources, such as intrinsic contaminations due to primordial radioisotopes and cosmogenic activation of the target material. In particular, we detect a 3.6keV X-ray line from the decay of 41-Ca with an activity of (26\pm4)\mu Bq, corresponding to a ratio 41-Ca/40-Ca=(2.2\pm0.3)\times10^{-16}., Comment: 7 pages, 12 figures

A method to stabilize cryogenic detectors with superconducting phase transition thermometers in their operating point is presented. Measurements of X-ray lines emitted by an 55 Fe X-ray fluorescence source showed an improvement in energy resolution from 230 to 133 eV on the 1.5 keV aluminium line with this technique. Furthermore the required set-up allows to simulate real events by injecting heat pulses into the thermometer and in this way to calibrate the detector and to monitor its long-term stability.

Diffusion of quasiparticles over distances up to 4 mm has been observed in various superconducting films. The quasiparticles were created by X-ray absorption in film strips with critical temperatures near 1 K and were detected in two superconducting phase transition thermometers at the ends of each strip. Position and energy of the absorbed X-rays as well as diffusion constants and lifetimes of the quasiparticles were determined. Very long lifetimes up to 9 ms allow the realization of large area phonon collector films on massive cryogenic particle detectors. Recently, with a first such detector a high efficiency of the phonon collection could be demonstrated.

CRESST-II, standing for Cryogenic Rare Events Search with Superconducting Thermometers phase II, is an experiment searching for Dark Matter. In the LNGS facility in Gran Sasso, Italy, a cryogenic detector setup is operated in order to detect WIMPs by elastic scattering off nuclei, generating phononic lattice excitations and scintillation light. The thermometers used in the experiment consist of a tungsten thin-film structure evaporated onto the CaWO4 absorber crystal. The process of evaporation causes a decrease in the scintillation light output. This, together with the need of a big-scale detector production for the upcoming EURECA experiment lead to investigations for producing thermometers on smaller crystals which are glued onto the absorber crystal. In our Run 31 we tested composite detectors for the first time in the Gran Sasso setup. They seem to produce higher light yields as hoped and could provide an additional time based discrimination mechanism for low light yield clamp events., Proceedings of the Thirteenth International Workshop on Low Temperature Detectors 4 pages, 9 figures

The alpha decay of $\n{{}^{210}Po}$ is a dangerous background to rare event searches. Here, we describe observations related to this alpha decay in the Cryogenic Rare Event Search with Superconducting Thermometers (CRESST). We find that lead nuclei show a scintillation light yield in our $\n{CaWO_4}$ crystals of $0.0142\pm0.0013$ relative to electrons of the same energy. We describe a way to discriminate this source of nuclear recoil background by means of a scintillating foil, and demonstrate its effectiveness. This leads to an observable difference in the pulse shape of the light detector, which can be used to tag these events. Differences in pulse shape of the phonon detector between lead and electron recoils are also extracted, opening the window to future additional background suppression techniques based on pulse shape discrimination in such experiments., Comment: 5 pages, 9 figures

Cryogenic calorimeters with superconducting phase transition (SPT) thermometers are extremely sensitive particle detectors. Some characteristics of SPT calorimeters such as linearity and dynamic range often suffer from the superconducting transition shape. The common way to improve the performances is to use the voltage bias to operate the SPT calorimeter in strong electrothermal feedback mode. This method does not allow us to optimize the noise, linearity and dynamic properties simultaneously. We have developed a novel SQUID circuit with thermal feedback which allows to improve the linearity, dynamic range and speed of the SPT calorimeter. Results obtained with a cryogenic calorimeter based on a tungsten thermometer are presented.

This work reports on the development of the first phonon detectors based on CaMoO4 and ZnWO4 scintillating crystals for the CRESST-II experiment. In particular, a novel technique for the production of the ZnWO4 phonon detector with a separate thermometer carrier was investigated. The influence of the thermal and mechanical treatment on the scintillation light output of CaMoO4 and ZnWO4 crystals at room temperature is discussed., Comment: 7 pages, 7 figures; to be published in Optical Materials

Many experiments in nuclear and particle physics would benefit from the development of a device capable of detecting non-ionizing events with a low energy threshold. In this context, we report on experimental tests of a detector based on the registration of nonequilibrium phonons. The device is composed of a silicon single crystal (size: 20×10×3 mm3) and of an array of superconducting tunnel junctions evaporated onto the surface of the crystal. The junctions serve as sensors for phonons created by absorption of nuclear radiation in the crystal. We show how pulse height analysis and the investigation of time differences between correlated pulses in different junctions can be used to obtain information about the point of absorption.

The CRESST experiment is looking for non-baryonic particle dark matter via nuclear scattering in CaWO4. The simultaneous measurement of the heat and the scintillation light generated by an event in a CaWO4 single crystal is used to discriminate between electron and nuclear recoils thanks to their different light output. This allows an efficient suppression of the electron recoil background. The set-up consists of modules with a 300 g CaWO4 crystal mounted in a reflective housing together with a light detector. The heat signal is read out using a superconducting transition-edge sensor (TES) made of tungsten evaporated directly on to the crystal that is operated at a few mK. Currently the second phase of the experiment is being set up at the Laboratori Nazionali del Gran Sasso in which it is planned to run 33 detector modules providing a total target mass of 10 kg. First test runs with prototype detectors have been successfully performed.

The ZEPLIN collaboration has recently published its first result presenting a maximum sensitivity of $1.1 \times 10^{-6}$ picobarn for a WIMP mass of $\approx$ 60 GeV. The analysis is based on a discrimination method using the different time distribution of scintillation light generated in electron recoil and nuclear recoil interactions. We show that the methodology followed both for the calibration of the ZEPLIN-I detector response and for the estimation of the discrimination power is not reliable enough to claim any background discrimination at the present stage. The ZEPLIN-I sensitivity appears then to be in the order of 10$^{-3}$ picobarn, three orders of magnitude above the claimed 1.1 10$^{-6}$ picobarn., 8 pages, 4 figures, minor corrections, two references updated, final version accepted in Physics Letters B

We are developing massive cryogenic detectors with low energy thresholds and high resolution for use in a direct Dark Matter search experiment. Our detector consists of a superconducting phase transition thermometer evaporated onto the surface of an absorber crystal. An energy resolution of 220 eV FWHM (for 6 keV X-rays) has been reached with a 31 g sapphire crystal using a proximity-effect thermometer. The latest results for sapphire detectors using tungsten superconducting phase transition thermometers, whose development is just beginning, are also presented. The planned further development and use of such detectors in a search for Dark Matter particles (WIMPs) is discussed, showing their advantages for low WIMP masses.

The low transition temperature of tungsten should allow fabrication of X-ray detectors combining high-energy resolution and enlarged absorber area (similar to1 mm(2)). We present first results obtained for lead and gold absorbers read out by tungsten superconducting phase transition thermometers (W-SPT) using a variety of detector geometries.

Data taken by CRESST with a cryogenic detector system based on 262 g sapphire crystals has been used to place limits on WIMP dark matter in the Galactic Halo. The experiment was especially sensitive for low-mass WIMPs with spin-dependent cross sections and improves on existing limits in this region. © 2002 Elsevier Science B.V. All rights reserved.

The sensitivity for WIMP detection can be improved by an ability to efficiently discriminate the γ and β backgrounds from the nuclear recoil signals. The CRESST phase II detectors will achieve this discrimination by means of simultaneous measurement of phonons and scintillation light. We report on the development of a 300 g detector module consisting of two separate calorimeters fitted with tungsten phase transition thermometers. A 300 g CaWO4 crystal serves as the target material in which a recoiling WIMP creates both phonons and scintillation light. Phonons are detected by a thermometer on the CaWO4 crystal. A second smaller detector in close proximity detects the scintillation light. Measurements with this setup will be presented.

The current status of CRESST (Cryogenic Rare Event Search using Superconducting Thermometers) and new results concerning the detector development are presented. The basic technique of CRESST is to search for particle Dark Matter (WIMPS, Weakly Interacting Massive particles) by the measurement of non-thermal phonons as created by WIMP-induced nuclear recoils. Combined with the newly developed method of simultaneous measurement of scintillation light, strong background discrimination is possible, resulting in a substantial increase in WIMP detection sensitivity. The short and long term perspectives of CRESST are discussed., Comment: 12 pages, 6 figures