Canfranc Underground Laboratory Research Articles

Searching for WIMPs with TREX-DM: achievements and challenges

The TREX-DM detector, a low background chamber with microbulk Micromegas readout, was commissioned in the Canfranc Underground Laboratory (LSC) in 2018. Since then, data taking campaigns have been carried out with argon and neon mixtures, at different pressures from 1 to 4 bar. By achieving a low energy threshold of 1 keV ee and a background level of 80 counts keV-1 kg-1 day-1 in the region from 1 to 7 keV ee , the experiment demonstrates its potential to search for low-mass WIMPs. Two of the most important challenges currently faced are the reduction of both, background level and energy threshold. With respect to the energy threshold, recently a new readout plane is being developed, based on the combination of Micromegas and GEM technologies, aiming to have a pre-amplification stage that would permit very low energy thresholds, close to the single-electron ionization energy. With respect to the background reduction, apart from studies to identify and minimize contamination population, a high sensitivity alpha detector is being developed in order to allow a proper material selection for the TREX-DM detector components. Both challenges, together with the optimization of the gas mixture used as target for the WIMP detection, will take TREX-DM to explore regions of WIMP's mass below 1 GeV c -2.

Canfranc biology platform: exploring life in cosmic silence

Deep underground laboratory infrastructures have extensively been used for exploring rare events, such as proton decay, dark matter searches or neutrino interactions, taking advantage of their large muon flux reduction. However, only very few investigations have evaluated the effects of low background radiation environments on living organisms. With this purpose, the Canfranc Underground Laboratory (LSC) launched the Biology Platform in 2021, which provides lab space for approved biology experiments. Two identical laboratories have been built (underground and on surface) to replicate biology experiments under the same conditions, with the main difference being the cosmic radiation background. The access protocol to use the LSC facilities includes two open calls per year and assigned time windows for executing the experimental program, which led to the first eight approved and already running experiments. We describe the scientific program of the Canfranc Biology Platform, which explores extremophiles, viral infection, immune system, multicellularity, development or aging in cosmic silence, and the first experimental results. The Platform also allows to observe the response of life to microgravity in absence of radiation, a key condition to explore life in space.

Test of 116CdWO4 and Li2MoO4 scintillating bolometers in the CROSS underground facility with upgraded detector suspension

In preparation for the CROSS experiment to search for double-beta (2β) decay of 100Mo, we upgraded a low-background facility at the Canfranc underground laboratory (Spain) by installing a magnetic damping-based detector suspension inside a pulse-tube cryostat. We tested the suspension in low-temperature (15 mK) measurements with two scintillating bolometers made of large-volume crystals of 116CdWO4 (reference of the set-up) and Li2MoO4 (R&D of the CLYMENE project in view of the CUPID 2β experiment), each coupled to a thin Ge bolometric light detector. Despite the evidence of a residual pulse-tube-induced noise, picked up by cabling, we achieved high performance with all tested devices. In particular, the energy resolution for 2615 keV γ-ray measured with both 116CdWO4 and Li2MoO4 bolometers is ∼6 keV FWHM, among the best-reported results for thermal detectors based on such compounds representing a great interest to searches for 2β decay in 116Cd (Q-value is 2813 keV) and 100Mo (3034 keV) respectively. Highly efficient particle identification (α vs. β/γ) is achieved also with the scintillating bolometer made of a low light yield crystal (Li2MoO4), thanks to the low noise (10 eV RMS) exhibited by the light detector exploiting the Neganov-Trofimov-Luke effect for signal amplification. We also found a rather high level of radiopurity in the Li2MoO4 crystal; only traces of 210Po and 226Ra were detected (∼0.1 mBq/kg each), while the 228Th activity is expected to be at least an order of magnitude lower, as well as a 40K activity is below 6 mBq/kg.

Li2100deplMoO4 Scintillating Bolometers for Rare-Event Search Experiments

We report on the development of scintillating bolometers based on lithium molybdate crystals that contain molybdenum that has depleted into the double-β active isotope 100Mo (Li2100deplMoO4). We used two Li2100deplMoO4 cubic samples, each of which consisted of 45-millimeter sides and had a mass of 0.28 kg; these samples were produced following the purification and crystallization protocols developed for double-β search experiments with 100Mo-enriched Li2MoO4 crystals. Bolometric Ge detectors were utilized to register the scintillation photons that were emitted by the Li2100deplMoO4 crystal scintillators. The measurements were performed in the CROSS cryogenic set-up at the Canfranc Underground Laboratory (Spain). We observed that the Li2100deplMoO4 scintillating bolometers were characterized by an excellent spectrometric performance (∼3–6 keV of FWHM at 0.24–2.6 MeV γs), moderate scintillation signal (∼0.3–0.6 keV/MeV scintillation-to-heat energy ratio, depending on the light collection conditions), and high radiopurity (228Th and 226Ra activities are below a few µBq/kg), which is comparable with the best reported results of low-temperature detectors that are based on Li2MoO4 using natural or 100Mo-enriched molybdenum content. The prospects of Li2100deplMoO4 bolometers for use in rare-event search experiments are briefly discussed.

Twelve-crystal prototype of Li2MoO4 scintillating bolometers for CUPID and CROSS experiments

An array of twelve 0.28 kg lithium molybdate (LMO) low-temperature bolometers equipped with 16 bolometric Ge light detectors, aiming at optimization of detector structure for CROSS and CUPID double-beta decay experiments, was constructed and tested in a low-background pulse-tube-based cryostat at the Canfranc underground laboratory in Spain. Performance of the scintillating bolometers was studied depending on the size of phonon NTD-Ge sensors glued to both LMO and Ge absorbers, shape of the Ge light detectors (circular vs. square, from two suppliers), in different light collection conditions (with and without reflector, with aluminum coated LMO crystal surface). The scintillating bolometer array was operated over 8 months in the low-background conditions that allowed to probe a very low, μBq/kg, level of the LMO crystals radioactive contamination by 228Th and 226Ra.

On Listening in to the Scientific Mundane

Scientific discovery often makes for a spectacular image or news story, as recent photographs of Sagittarius A*, a supermassive black hole at the centre of our own Milky Way, evidence. However, the mundane processes of scientific research, with their bureaucratic nuances, unsolvable conundrums, small talk, reporting, meetings, and seemingly inconsequential details, are often undocumented. Between January 2022 – May 2023 Rebecca Collins was artist-in-residence in B14, an office at the Institute for Theoretical Particle Physics at the Autonomous University of Madrid. Throughout the residency period she listened in to the mundane rhythms, atmospheres, and affects circulating among those who are trying to understand what took place in the first three minutes of our universe. She dedicated the majority of her efforts to listening in to dark matter – at once an ongoing scientific conundrum and totally mundane substance. In Spain, international teams of physicists use specifically designed technological apparatus and laboratories to look for dark matter, an abundant yet elusive undetected particle present in our everyday lives. Field notes from visits to the Canfranc Underground Laboratory, situated below the Pyrenees mountains, and the Laboratory of Acoustics for the Detection of Astroparticles, positioned 2.5 kilometres below the surface of the Mediterranean Sea serve to further reflect on the process-driven efforts of research into new physics. Anecdotes and autoethnographic writing from the situated and subjective experience of the author aims to understand how institutions and individuals dedicated to the investigation of new physics enable the extraordinary and the utterly mundane to coexist. Ultimately, the article considers how interdisciplinary encounters, anecdotes, conversations and site-based accounts constitute a practice-based research methodology that strives for collective practices of uncertainty, and a politics of indeterminacy.

Improving ANAIS-112 sensitivity to DAMA/LIBRA signal with machine learning techniques

The DAMA/LIBRA observation of an annual modulation in the detection rate compatible with that expected for dark matter particles from the galactic halo has accumulated evidence for more than twenty years. It is the only hint of a direct detection of the elusive dark matter, but it is in strong tension with the negative results of other very sensitive experiments, requiring ad-hoc scenarios to reconcile all the present experimental results. Testing the DAMA/LIBRA result using the same target material, NaI(Tl), removes the dependence on the particle and halo models and is the goal of the ANAIS-112 experiment, taking data at the Canfranc Underground Laboratory in Spain since August 2017 with 112.5 kg of NaI(Tl). At very low energies, the detection rate is dominated by non-bulk scintillation events and careful event selection is mandatory. This article summarizes the efforts devoted to better characterize and filter this contribution in ANAIS-112 data using a boosted decision tree (BDT), trained for this goal with high efficiency. We report on the selection of the training populations, the procedure to determine the optimal cut on the BDT parameter, the estimate of the efficiencies for the selection of bulk scintillation in the region of interest (ROI), and the evaluation of the performance of this analysis with respect to the previous filtering. The improvement achieved in background rejection in the ROI, but moreover, the increase in detection efficiency, push the ANAIS-112 sensitivity to test the DAMA/LIBRA annual modulation result beyond 3σ with three-year exposure, being possible to reach 5σ by extending the data taking for a few more years than the scheduled 5 years which were due in August 2022.

The Canfranc Axion Detection Experiment (CADEx): search for axions at 90 GHz with Kinetic Inductance Detectors

We propose a novel experiment, the Canfranc Axion Detection Experiment (CADEx), to probe dark matter axions with masses in the range 330–460 μeV, within the W-band (80–110 GHz), an unexplored parameter space in the well-motivated dark matter window of Quantum ChromoDynamics (QCD) axions. The experimental design consists of a microwave resonant cavity haloscope in a high static magnetic field coupled to a highly sensitive detecting system based on Kinetic Inductance Detectors via optimized quasi-optics (horns and mirrors). The experiment is in preparation and will be installed in the dilution refrigerator of the Canfranc Underground Laboratory. Sensitivity forecasts for axion detection with CADEx, together with the potential of the experiment to search for dark photons, are presented.

Long term measurement of the ^{222}Rn concentration in the Canfranc Underground Laboratory

We report the results of 6 years (2013–2018) of measurements of ^{222}Rn air concentration, relative humidity, atmospheric pressure and temperature in the halls A, B and C of the Canfranc Underground Laboratory (LSC). We have calculated all the Pearson correlation coefficients among these parameters and we have found a positive correlation between the ^{222}Rn concentration and the relative humidity. Both correlated variables show a seasonal periodicity. The joint analysis of laboratory data and 4 years (2015–2018) of the meteorological variables outside the laboratory shows the correlation between the ^{222}Rn concentration and the outside temperature. The collected information stresses the relevance of designing good Rn-mitigation strategies in current and future experiments at LSC; in particular, we have checked for two years (2017–2018) the good performance of the mitigation procedure of the ANAIS-112 experiment. Finally, we have monitored (2019–2021) for 2 years of live time, the radon-free air provided by the radon abatement system installed in the laboratory.

Long-term evolution of the neutron rate at the Canfranc Underground Laboratory

We report results on the long-term variation of the neutron counting rate at the Canfranc Underground Laboratory, of importance for several low-background experiments installed there, including rare-event searches. The measurement campaign was performed employing the High Efficiency Neutron Spectrometry Array (HENSA) mounted in Hall A and lasted 412 live days. The present study is the first long-term measurement of the neutron rate with sensitivity over a wide range of neutron energies (from thermal up to 0.1 GeV and beyond) performed in any underground laboratory so far. Data on the environmental variables inside the experimental hall (radon concentration, air temperature, air pressure and humidity) were also acquired during all the measurement campaign. We have investigated for the first time the evolution of the neutron rate for different energies of the neutrons and its correlation with the ambient variables.

Dark Matter Searches Using NaI(Tl) at the Canfranc Underground Laboratory: Past, Present and Future

Sodium Iodide Thallium doped (NaI(Tl)) scintillation detectors have been applied to the direct searches for dark matter since the 1980s and have produced one of the most challenging results in the field—the observation by the DAMA/LIBRA collaboration of an annual modulation in the detection rate for more than twenty cycles. This result is very difficult to reconcile with negative results derived from other experiments using a large variety of target materials and detection techniques. However, it has been neither confirmed nor refuted in a model independent way up to the present. Such a model independent test of the DAMA/LIBRA result is the goal of the ANAIS-112 experiment, presently in the data taking phase at the Canfranc Underground Laboratory in Spain. ANAIS-112 design and operation leans on the expertise acquired at the University of Zaragoza in direct searches for Dark Matter particles using different targets and techniques and in particular using NaI(Tl) scintillation detectors for about thirty years, which are reviewed in the first section of this manuscript. In addition to presenting the status and more recent results of the ANAIS-112 experiment, open research lines, continuing this effort, will be presented.

First results from the HENSA/ANAIS collaboration at the Canfranc Underground Laboratory

The HENSA/ANAIS collaboration aims for the precise determination of the neutron flux that could affect ANAIS-112, an experiment looking for the dark matter annual modulation using NaI(Tl) scintillators. In this work, the first measurements of the neutron flux and Monte Carlo simulations of the neutron spectrum are reported.

Measurement of the neutron flux at the Canfranc Underground Laboratory with HENSA

We have performed a long-term measurement of the neutron flux with the High Efficiency Neutron Spectrometry Array HENSA in the Hall A of the Canfranc Underground Laboratory. The Hall A measurement campaign lasted from October 2019 to March 2021, demonstrating an excellent stability of the HENSA setup. Preliminary results on the neutron flux from this campaign are presented for the first time. In Phase 1 (113 live days) a total neutron flux of 1.662 × 10−5 cm−2 s−1 is obtained. Our results are in good agreement with those from our previous shorter measurement where a reduced experimental setup was employed.

Machine-learning techniques applied to three-year exposure of ANAIS–112

ANAIS is a direct dark matter detection experiment aiming at the confirmation or refutation of the DAMA/LIBRA positive annual modulation signal in the low energy detection rate, using the same target and technique. ANAIS–112, located at the Canfranc Underground Laboratory in Spain, is operating an array of 3×3 ultrapure NaI(Tl) crystals with a total mass of 112.5 kg since August 2017. The trigger rate in the region of interest (1-6 keV) is dominated by non-bulk scintillation events. In order to discriminate these noise events from bulk scintillation events, robust filtering protocols have been developed. Although this filtering procedure works very well above 2 keV, the measured rate from 1 to 2 keV is about 50% higher than expected according to our background model, and we cannot discard non-bulk scintillation events as responsible of that excess. In order to improve the rejection of noise events, a Boosted Decision Tree has been developed and applied. With this new PMT-related noise rejection algorithm, the ANAIS–112 background between 1 and 2 keV is reduced by almost 30%, leading to an increase in sensitivity to the annual modulation signal. The reanalysis of the three years of ANAIS–112 data with this technique is also presented.

Annual modulation results from three-year exposure of ANAIS-112

ANAIS-112 is a dark matter direct detection experiment that operates 112 kg of NaI(Tl) scintillators at the Canfranc Underground Laboratory (LSC, Spain). Its main goal is to test in a model independent way one of the most puzzling results in the present particle physics scenario: the DAMA/LIBRA observation of an annual modulation in the detection rate compatible with that expected for dark matter. This signal is in strong tension with the negative results of other very sensitive experiments. However, until recently a direct comparison using the same target material (NaI(Tl)) was lacking. ANAIS-112 has been taking data since August 2017 in stable conditions with excellent performance. Results from the first three years are compatible with the absence of modulation and incompatible with the DAMA/LIBRA measured modulation at more than 2.5σ C.L. This result supports the projected goal of reaching a 3σ sensitivity to the DAMA/LIBRA result for the scheduled five-year operation.

Background model of the ANAIS-112 dark matter experiment

The ANAIS (Annual modulation with NaI(Tl) Scintillators) experiment aims at the confirmation or refutation of the DAMA/LIBRA positive annual modulation signal in the low energy detection rate. ANAIS-112, consisting of nine 12.5 kg NaI(Tl) modules, is taking data since August, 2017 at the Canfranc Underground Laboratory (LSC) in Spain. Results from the analysis of three years of data are compatible with the absence of modulation. The background model developed for all nine ANAIS-112 detectors was established from commissioning data and non-blinded events in the first year of data taking. Now, background characterization is being improved profiting from the larger accumulated exposure available. Here, the background model is described and comparisons of model and measurements for energy spectra and counting rate time evolution for three-year exposure (considering different analysis conditions) are presented.

The Positron Passport: An Essay-Poem in Quantum Poetics

This essay-poem develops the author's ongoing transdisciplinary examination of her integrated artistic practice and theory known as ‘quantum poetics’, investigating shared principles in poetry and science with the aim of reinventing common notions of spacetime, language, and reality. Topics touched upon include her research in particle physics at the European Organization for Nuclear Research (CERN) and Canfranc Underground Laboratory, the uncertainty principle in quantum theory and aesthetic ambiguity, Werner Heisenberg's essays on language and science, the reader of a literary text in relation to an observation in quantum theory, string theory and poetry, the asymmetry of matter and antimatter in the known universe in relation to the imagination, and the poethics of science. Using a cross-genre form that includes poetry, creative nonfiction, and academic scholarship identified as an essay-poem, the author writes in ‘windows’, justified text blocks that transition into and out of original poetry and quoted material by writers and scientists. One purpose of these windows is to treat the spacetime of the page as a literary device, one that visually foregrounds the material construct of literary language.

Annual modulation results from three-year exposure of ANAIS-112

ANAIS (Annual modulation with NaI Scintillators) is a dark matter direct detection experiment consisting of 112.5 kg of NaI(Tl) detectors in operation at the Canfranc Underground Laboratory (LSC), in Spain, since August 2017. ANAIS' goal is to confirm or refute in a model independent way the DAMA/LIBRA positive result: an annual modulation in the low-energy detection rate having all the features expected for the signal induced by dark matter particles in a standard galactic halo. This modulation, observed for about 20 years, is in strong tension with the negative results of other very sensitive experiments, but a model-independent comparison is still lacking. By using the same target material, NaI(Tl), such comparison is more direct and almost independent on dark matter particle and halo models. Here, we present the annual modulation analysis corresponding to three years of ANAIS data (for an effective exposure of 313.95 kg$\times$y), applying a blind procedure which updates that developed for the 1.5 years analysis, and later applied to 2 years. The analysis also improves the background modelling in the fitting of the region of interest rates. We obtain for the best fit in the [1-6] keV ([2-6] keV) energy region a modulation amplitude of -0.0034$\pm$0.0042 cpd/kg/keV (0.0003$\pm$0.0037 cpd/kg/keV), supporting the absence of modulation in our data, and incompatible with DAMA/LIBRA result at 3.3 (2.6) $\sigma$, for a sensitivity of 2.5 (2.7) $\sigma$. Moreover, we include two complementary analyses: a phase-free annual modulation search and the exploration of the possible presence of a periodic signal at other frequencies. Finally, we carry out several consistency checks of our result, and we update the ANAIS-112 projected sensitivity for the scheduled 5 years of operation.

A CUPID Li2100MoO4 scintillating bolometer tested in the CROSS underground facility

A scintillating bolometer based on a large cubic Li2100MoO4 crystal (45 mm side) and a Ge wafer (scintillation detector) has been operated in the CROSS cryogenic facility at the Canfranc underground laboratory in Spain. The dual-readout detector is a prototype of the technology that will be used in the next-generation 0ν2β experiment CUPID . The measurements were performed at 18 and 12 mK temperature in a pulse tube dilution refrigerator. This setup utilizes the same technology as the CUORE cryostat that will host CUPID and so represents an accurate estimation of the expected performance. The Li2100MoO4 bolometer shows a high energy resolution of 6 keV FWHM at the 2615 keV γ line. The detection of scintillation light for each event triggered by the Li2100MoO4 bolometer allowed for a full separation (∼8σ) between γ(β) and α events above 2 MeV . The Li2100MoO4 crystal also shows a high internal radiopurity with 228Th and 226Ra activities of less than 3 and 8 μBq/kg, respectively. Taking also into account the advantage of a more compact and massive detector array, which can be made of cubic-shaped crystals (compared to the cylindrical ones), this test demonstrates the great potential of cubic Li2100MoO4 scintillating bolometers for high-sensitivity searches for the 100Mo 0ν2β decay in CROSS and CUPID projects.

Uncertainty estimation in the forecasting of the 222Rn radiation level time series at the Canfranc Underground Laboratory

Abstract Nowadays decision making is strongly supported by the high-confident point estimations produced by deep learning algorithms. In many activities, they are sufficient for the decision-making process. However, in some other cases, confidence intervals are required too for an appropriate decision-making process. In this work, a first attempt to generate point estimations with confidence intervals for the $^{222}$Rn radiation level time series at Canfranc Underground Laboratory is presented. To predict the low-radiation periods allows correctly scheduling the unshielded periods for maintenance operations in the experiments hosted in this facility. This should minimize the deposition of radioactive dust on the exposed surfaces during these unshielded periods. An approach based on deep learning with stochastic regulation is evaluated in the forecasting of point estimations and confidence intervals of the $^{222}$Rn time series and compared with a second approach based on Gaussian processes. As a consequence of this work, an evaluation of the capacity of Gaussian process and deep learning with stochastic regularization for generating point estimations and their confidence intervals for this time series is stated.