Superconducting detectors for rare event searches in experimental astroparticle physics

Superconducting detectors have become an important tool in experimental astroparticle physics, which seeks to provide a fundamental understanding of the Universe. In particular, such detectors have demonstrated excellent potential in two challenging research areas involving rare event search experiments, namely, the direct detection of dark matter and the search for neutrinoless double beta decay. Here, we review the superconducting detectors that have been and are planned to be used in these two categories of experiments. We first provide brief histories of the two research areas and outline their significance and challenges in astroparticle physics. Then, we present an extensive overview of various types of superconducting detectors with a focus on sensor technologies and detector physics, which are based on calorimetric measurements and heat flow in the detector components. Finally, we introduce leading experiments and discuss their future prospects for the detection of dark matter and the search for neutrinoless double beta decay employing superconducting detectors

Cryogenic Heat-Light Detection System for 1-cm3 Scintillating Crystals

We have developed a cryogenic heat and light detection system to investigate phonon and scintillation properties of scintillating crystals for rare event search experiments. The detector setup is designed to utilize a 1 × 1×1 cm3 scintillating crystal as a target material. A 1.5 × 1.5 × 0.05 cm3 Ge wafer is used as the absorber of the light detection. Metallic magnetic calorimeters are employed to measure heat and scintillation-light signals of the scintillating crystal, simultaneously, at millikelvin temperatures. This measurement setup is motivated to characterize various types of scintillation crystals in a standard coupon size for a final selection of the crystal compounds to be used for a rare event search experiment. We present the first measurement for a calcium molybdate crystal doped with niobium in the test setup of heat–light detection. Clear particle identification was obtained in comparison of relative amplitude ratios of the phonon and scintillation signals. Moreover, alpha- and electron-induced events showed difference in their pulse shapes of phonon and scintillation signals. We discuss the usage of this setup for the AMoRE 0 search experiment. © 2018 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permissio

Low temperature property study of MMCs used for neutrinoless double beta decay

© 2021 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. We present a comparison of the two types of metallic magnetic calorimeters (MMCs) developed for a large-scale neutrinoless double beta decay (0νββ) search experiment. As high resolution micro-calorimeters,MMCsemploy micro-fabricated superconducting circuits to measure the changes in magnetization of a paramagnetic sensor material. We constructed two alpha spectrometers with two MMC sensors made of Au:Er and Ag:Er (i.e., gold and silver alloys with small concentrations of Er). A piece of gold foil with a heat capacity comparable to that of 350 g CaMoO4 crystal near 10 mK was used as the absorber for each alpha spectrometer. These detector setups allowed us to investigate the temperature dependence of magnetization for the different sensor materials over a wide temperature range with various amounts of field current. The magnetizationmeasurements for both the Au:Er and Ag:Er sensors were in good agreement with calculations for field currents of up to 100 mA. Moreover, the measured and estimated pulse heights of alpha events agreed with each other, and were compared between the different sensor materials.We discuss howthe excess heat capacity fromthe nuclear spins in Au:Er influences the pulse size and shape in calorimetric detection. Moreover, we describe the benefit of using Ag:Er sensors in thermal calorimeters with large crystal absorbers in a 0νββ search experiment.11Nsciescopu

Structural and Magnetic Properties of Tetragonal Mn1.19Fe0.81As Thin Film Grown on Si(001)

We have successfully grown MnxFe2-xAs (x = 1.19) thin film on Si(001) substrate by molecular beam epitaxy. Reflection high-energy electron diffraction (RHEED) and X-ray diffraction (XRD) studies indicate the rough film surface and c-axis orientation in a tetragonal crystal structure. Mn1.19Fe0.81As film exhibited ferrimagnetic ordering at room temperature, which is supported by magnetization, magnetoresistance and anomalous-Hall-effect measurements.ope

Vibration Mitigation for a Cryogen-Free Dilution Refrigerator for the AMoRE-Pilot Experiment

The Advanced Mo-based Rare process Experiment utilizes a cryogen-free dilution refrigerator to operate its low-temperature detectors. Mechanical vibration originating from its pulse tube refrigerator can affect the detector performance. A mechanical filter system has been installed between the 4K and still plates with eddy current dampers in addition to a spring-loaded damping system previously installed below the mixing chamber plate of the cryostat. The filters significantly mitigated vibrations and improved the detector signals. © 2018 Springer Science+Business Media, LLC, part of Springer Natur

A Lab-Scale Experiment for keV Sterile Neutrino Search

We developed a simple small-scale experiment to measure the beta decay spectrum of H-3. The aim of this research is to investigate the presence of sterile neutrinos in the keV region. Tritium nuclei were embedded in a 1x1x1 cm(3) LiF crystal from the Li-6(n,alpha)H-3 reaction. The energy of the beta electrons absorbed in the LiF crystal was measured with a magnetic microcalorimeter at 40 mK. We report a new method of sample preparation, experiments, and analysis of H-3 beta measurements. The spectrum of a 10-hour measurement agrees well with the expected spectrum of H-3 beta decay. The analysis results indicate that this method can be used to search for keV-scale sterile neutrinos.11Nsciescopu

Study on Phonon Amplification of Neganov–Luke Light Detectors

We report progress on the development of a light detector with Neganov–Luke (NL) phonon amplification. Double comb-like electrodes were fabricated on an intrinsic Si wafer to apply an electric field. A metallic magnetic calorimeter was used for a sensitive measurement of the temperature increase originating from the light absorption in the wafer and NL phonon amplification. The NL light detector was applied to the simultaneous detection of heat and light signals from a ZnWO 4 scintillating crystal. Clear amplification of the light signals was obtained for various voltages applied to the electrodes, while no change in the heat signals was observed. The voltage dependence of the measured gain was investigated for a few efficiency parameters, such as the saturation voltage required to suppress the recombination of electron-hole pairs and the heat generation efficiency of the NL effect11Nsciescopu

An MMC-Based Temperature Control System for a Long-Term Data Collection

We developed a two-stage temperature control system for a long-term stable measurement of AMoRE neutrinoless double beta decay experiment using a dilution refrigerator. The first-stage control was made with a standard PID system using an AC bridge with a ruthenium oxide thermometer as the main thermometer of the mixing chamber plate. The second-stage control was obtained with a magnetic microcalorimeter (MMC) that is configured as a sensitive thermometer for a detector tower, the main experiment. Under single-stage temperature control on the temperature of the mixing chamber plate only with the RuO2 thermometer, the MMC recorded temperature stability of the detector plate of 9 mu K rms over 100 min. Under two-stage temperature control, with the first-stage of the mixing chamber plate at 11 mK via the RuO2 thermometer and the second-stage of the detector plate at 12 mK via the MMC, the MMC recorded a temperature stability of 0.5 mu K rms over 100 min. Moreover, the heat channels of the AMoRE experiment obtained considerable improvement in energy resolutions when switching from single-stage (RuO2) to two-stage (RuO2 + MMC) control.11Nsciescopu