Cryogenic Dark Matter Search Experiment Research Articles

CUTE: A Cryogenic Underground TEst facility at SNOLAB

Low-temperature cryogenics open the door for a range of interesting technologies based on features like superconductivity and superfluidity, low-temperature phase transitions or the low heat capacity of non-metals in the milli-Kelvin range. Devices based on these technologies are often sensitive to small energy depositions as can be caused by environmental radiation. The Cryogenic Underground TEst facility (CUTE) at SNOLAB is a platform for testing and operating cryogenic devices in an environment with low levels of background. The large experimental chamber (O(10) L) reaches a base temperature of ∼ 12 mK; it can hold a payload of up to ∼ 20 kg and provides a radiogenic background event rate as low as a few events/kg/keV/day in the energy range below about 100 keV, as well as a negligible muon rate (O1)/month). CUTE was designed and built in the context of the Super Cryogenic Dark Matter Search experiment (SuperCDMS) that uses cryogenic detectors to search for interactions of dark matter particles with ordinary matter. The facility has been used to test SuperCDMS detectors since its commissioning in 2019. In 2021, it was handed over to SNOLAB to become a SNOLAB user facility after the completion of the testing of detectors for SuperCDMS. The facility will be available for projects that benefit from these special conditions, based on proposals assessed for their scientific and technological merits. This article describes the main design features and operating parameters of CUTE.

Estimation of Interaction Locations in Super Cryogenic Dark Matter Search Detectors Using Genetic Programming-Symbolic Regression Method

The Super Cryogenic Dark Matter Search (SuperCDMS) experiment is used to search for Weakly Interacting Massive Particles (WIMPs)—candidates for dark matter particles. In this experiment, the WIMPs interact with nuclei in the detector; however, there are many other interactions (background interactions). To separate background interactions from the signal, it is necessary to measure the interaction energy and to reconstruct the location of the interaction between WIMPs and the nuclei. In recent years, some research papers have been investigating the reconstruction of interaction locations using artificial intelligence (AI) methods. In this paper, a genetic programming-symbolic regression (GPSR), with randomly tuned hyperparameters cross-validated via a five-fold procedure, was applied to the SuperCDMS experiment to estimate the interaction locations with high accuracy. To measure the estimation accuracy of obtaining the SEs, the mean and standard deviation (σ) values of R2, the root-mean-squared error (RMSE), and finally, the mean absolute error (MAE) were used. The investigation showed that using GPSR, SEs can be obtained that estimatethe interaction locations with high accuracy. To improve the solution, the five best SEs were combined from the three best cases. The results demonstrated that a very high estimation accuracy can be achieved with the proposed methodology.

Energy loss due to defect formation from 206Pb recoils in SuperCDMS germanium detectors

The Super Cryogenic Dark Matter Search experiment at the Soudan Underground Laboratory studied energy loss associated with defect formation in germanium crystals at mK temperatures using in situ 210Pb sources. We examine the spectrum of 206Pb nuclear recoils near its expected 103 keV endpoint energy and determine an energy loss of (6:08 ± 0:18)%, which we attribute to defect formation. From this result and using TRIM simulations, we extract the first experimentally determined average displacement threshold energy of 19.7−0.5+0.6 eV for germanium. This has implications for the analysis thresholds of future germanium-based dark matter searches.

Nuclear-recoil energy scale in CDMS II silicon dark-matter detectors

The Cryogenic Dark Matter Search (CDMS II) experiment aims to detect dark matter particles that elastically scatter from nuclei in semiconductor detectors. The resulting nuclear-recoil energy depositions are detected by ionization and phonon sensors. Neutrons produce a similar spectrum of low-energy nuclear recoils in such detectors, while most other backgrounds produce electron recoils. The absolute energy scale for nuclear recoils is necessary to interpret results correctly. The energy scale can be determined in CDMS II silicon detectors using neutrons incident from a broad-spectrum 252Cf source, taking advantage of a prominent resonance in the neutron elastic scattering cross section of silicon at a recoil (neutron) energy near 20 (182)keV. Results indicate that the phonon collection efficiency for nuclear recoils is 4.8−0.9+0.7% lower than for electron recoils of the same energy. Comparisons of the ionization signals for nuclear recoils to those measured previously by other groups at higher electric fields indicate that the ionization collection efficiency for CDMS II silicon detectors operated at ∼4V/cm is consistent with 100% for nuclear recoils below 20keV and gradually decreases for larger energies to ∼75% at 100keV. The impact of these measurements on previously published CDMS II silicon results is small.

Performance of the first 150 mm diameter Cryogenic silicon ionization detectors with contact-free electrodes

Cryogenic semiconductor detectors operated at temperatures below 100 mK are commonly used in particle physics experiments searching for dark matter. The largest such germanium and silicon detectors, with diameters of 100 mm and thickness of 33 mm, are planned for use by the Super Cryogenic Dark Matter Search (SuperCDMS) experiment at SNOLAB, Canada. Still larger individual detectors are being investigated to scale up the sensitive mass of future experiments. We present here the first results of testing two prototype 150 mm diameter silicon ionization detectors. The detectors are 25 mm and 33 mm thick with masses 1.7 and 2.2 times larger than those currently planned for SuperCDMS. These devices were operated with contact-free bias electrodes to minimize leakage currents which currently limit operation at high bias voltages. The results show promise for the use of such technologies in solid state cryogenic detectors.

Results from the Super Cryogenic Dark Matter Search Experiment at Soudan.

We report the result of a blinded search for weakly interacting massive particles (WIMPs) using the majority of the SuperCDMS Soudan data set. With an exposure of 1690kg d, a single candidate event is observed, consistent with expected backgrounds. This analysis (combined with previous Ge results) sets an upper limit on the spin-independent WIMP-nucleon cross section of 1.4×10^{-44} (1.0×10^{-44}) cm^{2} at 46 GeV/c^{2}. These results set the strongest limits for WIMP-germanium-nucleus interactions for masses >12 GeV/c^{2}.

Thermal conductance modeling and characterization of the SuperCDMS SNOLAB sub-Kelvin cryogenic system

The detectors of the Super Cryogenic Dark Matter Search experiment at SNOLAB (SuperCDMS SNOLAB) will operate in a seven-layered cryostat with thermal stages between room temperature and the base temperature of 15 mK. The inner three layers of the cryostat, which are to be nominally maintained at 1 K, 250 mK, and 15 mK, will be cooled by a dilution refrigerator via conduction through long copper stems. Bolted and mechanically pressed contacts, flat and cylindrical, as well as flexible straps are the essential stem components that will facilitate assembly/dismantling of the cryostat. These will also allow for thermal contractions/movements during cooldown of the sub-Kelvin system. To ensure that these components and their contacts meet their design thermal conductance, prototypes were fabricated and cryogenically tested. The present paper gives an overview of the SuperCDMS SNOLAB sub-Kelvin architecture and its conductance requirements. Results from the conductance measurements tests and from sub-Kelvin thermal modeling are discussed.

The cryogenics design of the SuperCDMS SNOLAB experiment

The Super Cryogenic Dark Matter Search (SuperCDMS) experiment is a direct detection dark matter experiment intended for deployment to the SNOLAB underground facility in Ontario, Canada. With a payload of up to 186 germanium and silicon crystal detectors operating below 15 mK, the cryogenic architecture of the experiment is complex. Further, the requirement that the cryostat presents a low radioactive background to the detectors limits the materials and techniques available for construction, and heavily influences the design of the cryogenics system. The resulting thermal architecture is a closed cycle (no liquid cryogen) system, with stages at 50 and 4 K cooled with gas and fluid circulation systems and stages at 1 K, 250 mK and 15 mK cooled by the lower temperature stages of a large, cryogen-free dilution refrigerator.This paper describes the thermal design of the experiment, including details of the cooling systems, mechanical designs and expected performance of the system under operational conditions.

Toward single electron resolution phonon mediated ionization detectors

Experiments seeking to detect rare event interactions such as dark matter or coherent elastic neutrino nucleus scattering are striving for large mass detectors with very low detection threshold. Using Neganov-Luke phonon amplification effect, the Cryogenic Dark Matter Search (CDMS) experiment is reaching unprecedented RMS resolutions of ∼14eVee. CDMSlite is currently the most sensitive experiment to WIMPs of mass ∼5GeV/c2 but is limited in achieving higher phonon gains due to an early onset of leakage current into Ge crystals. The contact interface geometry is particularly weak for blocking hole injection from the metal, and thus a new design is demonstrated that allows high voltage bias via vacuum separated electrode. With an increased bias voltage and a×2 Luke phonon gain, world best RMS resolution of sigma ∼7eVee for 0.25kg (d=75mm, h=1cm) Ge detectors was achieved. Since the leakage current is a function of the field and the phonon gain is a function of the applied voltage, appropriately robust interface blocking material combined with thicker substrate (25mm) will reach a resolution of ∼2.8eVee. In order to achieve better resolution of ∼ eV, we are investigating a layer of insulator between the phonon readout surface and the semiconductor crystals.

The SuperCDMS Soudan high threshold WIMP search and the planned SuperCDMS SNOLAB experiment

There is ample evidence that visible matter cannot account for a large component of the mass in the universe. Weakly Interacting Massive Particles (WIMPs) are one popular hypothesis to account for the missing mass. The Super Cryogenic Dark Matter Search (SuperCDMS) experiment is designed to directly detect WIMPs through interactions with a nucleus in a target crystal. The SuperCDMS detectors are instrumented with phonon and charge sensors, enabling excellent rejection of electron-recoil backgrounds. Approximately 3000 kg-days of exposure have been collected with the SuperCDMS Soudan experiment. We will describe the search for WIMPs with masses between 10-100 GeV and work towards the SuperCDMS SNOLAB experiment.

Low-threshold WIMP search at SuperCDMS

The Super Cryogenic Dark Matter Search (SuperCDMS) experiment aims to detecting nuclear recoils from weakly-interacting massive particles (WIMPs) by measuring phonon and ionization energy in crystalline Ge. It has been operating at the Soudan Underground Laboratory in Minnesota (USA) since March 2012 with improved background rejection capabilities with respect to CDMS II. A low-threshold analysis of the SuperCDMS data has been performed, allowing to explore WIMP masses below 30 GeV/c2. This is the first analysis using the full background rejection capabilities of SuperCDMS. In particular both phonon and ionization signals are used for defining a fiducial volume excluding events near any of the surfaces of the detectors. In addition, the background discrimination includes multivariate techniques optimized for several WIMP masses. The results are competitive with other low-threshold WIMP searches, and probe new parameter space for WIMP-nucleon scattering for WIMP masses between 4 and 6 GeV/c2.

Dark matter direct detection with SuperCDMS Soudan

The Cryogenic Dark Matter Search Experiment (CDMS) and its successor, SuperCDMS, have had a long history of establishing world-leading upper limits on the interaction of Weakly Interacting Massive Particles (WIMPs) with standard model nucleons. SuperCDMS uses arrays of cryogenic germanium detectors to achieve excellent discrimination between the nuclear recoils expected for WIMP interactions and radioactively produced electron recoils through the collection of ionization and athermal phonons. Recent analyses of the data collected from the current installation of Interleaved Z-Sensitive Ionization and Phonon (iZIP) detectors have probed new regions of the WIMP parameter space, particularly in the region of low-mass WIMP interactions. This paper will discuss the current work of the SuperCDMS collaboration.

Maximum likelihood analysis of low energy CDMS II germanium data

We report on the results of a search for a Weakly Interacting Massive Particle (WIMP) signal in low-energy data of the Cryogenic Dark Matter Search (CDMS~II) experiment using a maximum likelihood analysis. A background model is constructed using GEANT4 to simulate the surface-event background from $^{210}$Pb decay-chain events, while using independent calibration data to model the gamma background. Fitting this background model to the data results in no statistically significant WIMP component. In addition, we perform fits using an analytic ad hoc background model proposed by Collar and Fields, who claimed to find a large excess of signal-like events in our data. We confirm the strong preference for a signal hypothesis in their analysis under these assumptions, but excesses are observed in both single- and multiple-scatter events, which implies the signal is not caused by WIMPs, but rather reflects the inadequacy of their background model.

First direct limits on lightly ionizing particles with electric charge less than e/6.

While the standard model of particle physics does not include free particles with fractional charge, experimental searches have not ruled out their existence. We report results from the Cryogenic Dark Matter Search (CDMS II) experiment that give the first direct-detection limits for cosmogenically produced relativistic particles with electric charge lower than e/6. A search for tracks in the six stacked detectors of each of two of the CDMS II towers finds no candidates, thereby excluding new parameter space for particles with electric charges between e/6 and e/200.

PandaX-I result sets a stringent limit for low-mass dark matter particles

Astrophysical and cosmological observations show that about 27% of the energy in our universe comes from dark matter (DM). What is DM is an outstanding puzzle in science in the 21st century. The weakly interacting massive particles (WIMPs) have been by far the favored candidate for DM, although they cannot be accommodated in the standard model of strong and electroweak interactions. DM theory asserts that our solar system is bathed in the DM halo of the MilkyWay,withmillions ofWIMPs passing throughour body every second. Interactions of DM with ordinary matter are exceedinglyweak andmay be detected by sensitive equipment through the energy deposited in a detector by elastic scattering of WIMPs with the nuclei of ordinary matter. There are many such directsearch experiments around the world, trying to catch the faint signals released in the form of photons, electrons or heat using different technologies. Several experiments, such as the Dark Matter/Large Sodium Iodide Bulk for Rare Processes experiment in Italy, theCoherentGermanium Neutrino Technology and Cryogenic Dark Matter Search (CDMS) experiments in the USA and the Germanled Cryogenic Rare Event Search with Superconducting Thermometers experiment, have in recent years reported positive signals, which could be interpreted as light WIMPs. The first results published in Sci China Phys Mech Astron this year by the PandaX collaboration, however, downgrade these claims [1]. The PandaX (Particle AND Astrophysical Xenon Detector) collaboration is an international team of about 40 scientists led by Professor Xiangdong Ji from Shanghai Jiao Tong University (also affiliated with the University of Maryland). This is the first large-scale xenon DM search experiment carried out in the newly established China Jinping Underground Laboratory (CJPL) in Sichuan, China. CJPL is among the deepest underground laboratories in the world, and being well shielded from the cosmic ray background. Xenon is a noble gas, which becomes liquid at about 110◦ below zero Celsius. The current experiment uses about 120 kg of liquid xenon as the active target for WIMPs. The detector employs a technology called the dual-phase xenon time-projection chamber (TPC), enabling a 3D reconstruction of the events. This technology was shown to be one of the more promising technologies based on the similar 100 kg XENON DM project (XENON100) and the Large Underground Xenon experiments. It now offers improved detection sensitivity over a wide range of DM mass by two orders of magnitude compared with other experiments. The first stage of PandaX operations, the PandaX-I, intends to examine the curious signals of WIMPs in the low-mass region reported by previous experiments. Its detector is a pancake-shaped TPC designed for high photon-collection efficiency. PandaX-I’s first results are based on the data collected in 17.4 live days, with more than 4 million raw events recorded. After removing the low-quality events and narrowing the energy search window to the regions of interest, 46 events are seen in the central fiducial volume with 37 kg of liquid xenon. These events are consistent with signals from the background radiation, the paper reports. Without candidate WIMP DM events, PandaX-I sets a stringent limit for low-mass DM particles and effectively rules out the interpretation of positive experimental results previously reported. Together with the results reported by the China Dark matter Experiment led by scientists at Tsinghua University (also at CJPL) and the SuperCDMS experiments in the USA, PandaX has set one of the best limits for WIMP DM with low mass, as can be seen from the Fig. 1. PandaX’s first result demonstrates that China has become a competitive player in the search for DM, a Science News article commented. ‘It is very exciting to see that our detector has such a capability’, said Jianglai Liu, who led the data analysis and also contributed significantly to the detector construction. Indeed, the PandaX collaboration has since collected more than 75 days of data, which will have five times better detection sensitivity. The PandaX experiment is also upgrading its detector mass to 500 kg, and will commence operations in 2015. Meanwhile, XENON1T, a similar experiment but with a 1.5-ton detector mass, developed by a US-Europe collaboration

Systematics of Low Threshold Modulation Searches in DMS II

The Cryogenic Dark Matter Search experiment (CDMS II) used underground-based germanium and silicon detectors to search for the scattering of Weakly Interacting Massive Particles (WIMPs), which are among the leading candidates for the dark matter component of the universe. Using the ionization and athermal phonons measured in particle interactions, CDMS II was able to achieve excellent discrimination between the nuclear recoils expected for WIMP interactions and radioactively produced electron recoils. With the rise of interest in the low energy interactions of light mass WIMPs, the SuperCDMS collaboration has undertaken a search for an annually modulating signal at low thresholds in the CDMS II data. Previous results detailed the analysis of data from eight germanium detectors over the course of six runs, to thresholds of 5 keVnr (nuclear recoil equivalent energy). We will discuss the impact of systematics at these low thresholds and their implications for thresholds down to 2.27 keVnr.

Light NMSSM neutralino dark matter in the wake of CDMS II and a 126 GeV Higgs boson

Recent results from the Cryogenic Dark Matter Search (CDMS) experiment have renewed interest in light dark matter with a large spin-independent neutralino-nucleon scattering cross-section. Here, we examine the regions of the Next-to-MSSM (NMSSM) capable of producing a light neutralino with a large spin-independent scattering cross-section, with the scattering mediated by a very light singlet-like scalar, and a 126 GeV Standard Model-like Higgs consistent with the LHC results, while satisfying other relevant cosmological, flavor and collider constraints. We focus on two different scenarios for annihilation in the early universe, namely annihilation mediated by (1) a light scalar or by (2) a light pseudo-scalar. As expected, both cases are highly constrained. Nevertheless, we find that there persists potentially viable parameter space to accommodate either scenario. In the first, accidental cancellations in the couplings allow for a SM-like Higgs with a total width and invisible branching fraction compatible with the observed Higgs boson. Alternatively, the second scenario can occur in regions featuring smaller branching fractions of the SM-like Higgs to pairs of light scalars, pseudoscalars, and neutralinos without cancellations. The strongest constraints in both cases come from rare meson decays and exotic decays of the SM-like Higgs boson into neutralinos and light, CP-even Higgs pairs. We outline the relevant parameter space for both scenarios and comment on prospects for future discovery with various experiments.

Quasiparticle Diffusion in Al Films Coupled to Tungsten Transition Edge Sensors

We report recent results obtained from several W/Al test devices on Si wafers fabricated specifically to better understand energy collection in phonon sensors used for the Cryogenic Dark Matter Search (CDMS) experiment. The devices under study consist of three different lengths of 250 \(\upmu \)m-wide by 300 nm-thick Al absorber films, coupled to 250 \(\upmu \)m x 250 \(\upmu \)m (40 nm thick) W-TESs at each end of the Al film. An \(^{55}\)Fe source was used to excite a NaCl reflector producing 2.6 keV Cl X-rays that were absorbed in our test device after passing through a collimator. The impinging X-rays broke Cooper pairs in the Al film, producing quasiparticles that we detected after they propagated into the W-TESs. We studied the diffusion of these quasiparticles in the Al, trapping effects in the Al film, and energy transmission at the Al/W interfaces.

Extending the Fermi-LAT Data Processing Pipeline to the Grid

The Data Handling Pipeline (“Pipeline”) has been developed for the Fermi Gamma-Ray Space Telescope (Fermi) Large Area Telescope (LAT) which launched in June 2008. Since then it has been in use to completely automate the production of data quality monitoring quantities, reconstruction and routine analysis of all data received from the satellite and to deliver science products to the collaboration and the Fermi Science Support Center. Aside from the reconstruction of raw data from the satellite (Level 1), data reprocessing and various event-level analyses are also reasonably heavy loads on the pipeline and computing resources. These other loads, unlike Level 1, can run continuously for weeks or months at a time. In addition it receives heavy use in performing production Monte Carlo tasks.In daily use it receives a new data download every 3 hours and launches about 2000 jobs to process each download, typically completing the processing of the data before the next download arrives. The need for manual intervention has been reduced to less than 0.01% of submitted jobs.The Pipeline software is written almost entirely in Java and comprises several modules. The software comprises web-services that allow online monitoring and provides charts summarizing work flow aspects and performance information. The server supports communication with several batch systems such as LSF and BQS and recently also Sun Grid Engine and Condor. This is accomplished through dedicated job control services that for Fermi are running at SLAC and the other computing site involved in this large scale framework, the Lyon computing center of IN2P3. While being different in the logic of a task, we evaluate a separate interface to the Dirac system in order to communicate with EGI sites to utilize Grid resources, using dedicated Grid optimized systems rather than developing our own. More recently the Pipeline and its associated data catalog have been generalized for use by other experiments, and are currently being used by the Enriched Xenon Observatory (EXO), Cryogenic Dark Matter Search (CDMS) experiments as well as for Monte Carlo simulations for the future Cherenkov Telescope Array (CTA).

Results and Prospects for the Cryogenic Dark Matter Search (CDMS) Experiment

The Cryogenic Dark Matter Search (CDMS) experiment, located at the Soudan underground mine, operated 30 low-temperature Ge and Si detectors for several years to search for Weakly Interacting Massive dark matter Particles (WIMPs). Due to their excellent background discrimination power and low energy threshold, our detectors have provided world-leading sensitivity for WIMP-nucleon interactions for most of the past decade over a large WIMP mass range. The final exposure of our CDMS II detectors yielded two candidate events, with an expected background of 0.9 ± 0.2 events, and this result was published in March 2010 in Science. A reanalysis of 8 Ge detectors with a lowered, 2 keV recoil energy threshold, provided increased sensitivity to interactions from WIMPs with masses below 10 GeV/c2 and excluded possible low-mass WIMP signals from the DAMA/LIBRA and CoGeNT experiments. The CDMS collaboration is moving forward with the SuperCDMS experiments at Soudan and SNOLAB with the goal of probing the zeptobarn scale and beyond over the next decade. To achieve this goal, a new generation of larger mass detectors with interleaved geometry for the phonon and ionization readout has been developed.