The ARIA project and the search for Dark Matter

The search for Dark Matter (DM) is one of the most fascinating challenges of modern physics and astrophysics, but also one of the most difficult altogether. A large ensemble of indirect cosmological observations has established its presence and the fact that DM is about five times more abundant than ordinary matter: though not “seen” yet, its gravitational effects represent an unquestionable proof. Its nature is totally unknown: DM does not fit into the “Standard Model” of particle physics. Today, several experiments across the world are striving to perform a first direct observation of DM, with new experiments operating from the deep throes of underground to outer space. The race to the first discovery is pushing researchers across the globe to open new pathways, with a combination of ingenuity and technological innovation.

The existence of DM was first postulated in the 1930s to justify the anomalies of the rotation pattern in clusters of galaxies. Today, the evidence for its presence extends to nearly every single advanced cosmological observable. The ensemble of observations indicated that DM is not only heavy but also “cold”, i.e., moving at speed considerably slower than that of light and comparable to the orbital speed of galaxies and stars. One tantalizing solution is the possibility that DM be formed by a new generation of particles, massive yet interacting very weakly, akin to very massive neutrinos. This class of DM candidates goes under the name of “WIMPs” for Weakly Interacting Massive Particles.

1 The search for Dark Matter at the Gran Sasso National Laboratories

If DM is indeed in the form of WIMPs, it may be identified by its ultra-weak interactions on target nuclei, inducing nuclear recoils. Discovery may therefore come through the observation of extremely rare DM interactions with an ultra-pure, low-radioactivity target detector, optimized to isolate and positively identify nuclear recoils from the white noise of radioactive events induced by natural radioactivity. Two necessary pre-conditions apply in order to make a success in this enterprise possible at all.

First of all, the white noise from natural radioactivity must be minimized to preserve a chance at all to isolate and observe the nuclear recoils induced by DM. The first step requires taking care of the cosmic radiation. The Earth is continually struck by cosmic rays, particles of galactic and extragalactic origin, which create background signals that make the observation of DM on the Earth’s surface simply impossible. The search for DM finds in the Laboratori Nazionali del Gran Sasso (LNGS) of the Istituto Nazionale di Fisica Nucleare (INFN) a cutting-edge host facility for advanced experiments. Today LNGS is the largest and most important underground research center in the world. LNGS was designed and built in the 1980s with the aim of offering the best site for neutrino and DM investigations, exploiting the protection from cosmic radiation offered by the 1400 meters of rock shield, which stops and reduces most of the cosmic radiation. The rock overburden of LNGS reduces the cosmic rays by a factor of one million.

Far from surprising, LNGS is today the host to the largest concentration of DM experiments, including: the sodium iodide detectors of the DAMA family, looking for Dark Matter from within its ultra-low background shield; the scintillating bolometers operated by the CRESST Collaboration, exploiting a unique combination of signals; the prototype of the SABRE detector, operating sodium iodide crystals within a liquid scintillator veto; last, XENON Collaboration detectors, which through four different generations of ever increasing mass, size, and sensitivity, have come to hold today the world’s current best sensitivity and records in WIMP DM searches.

2 The Global Argon Dark Matter Collaboration

The second necessary condition for the observation of Dark Matter is the ability of rejecting natural radioactivity in favor of the identification and selection of nuclear recoils. Nuclear recoils, as stated above, are the most likely outcome of the direct interactions of DM with the target nuclei of detectors. The most ubiquitous events produced by natural radioactivity, instead, involve direct interactions on the electrons surrounding the nuclei. The two interactions, owing to the marked difference in mass between electrons and nuclei, result in different structures for the ensuing ionizing tracks. The tracks left by nuclear recoils are much shorter and denser than those induced by electrons, which are sufficiently close to tracks near the minimum of ionization. The difference in ionization density is at the root of the ability of any detector in separating nuclear recoils from minimum ionizing electrons.

While nearly all DM detectors are endowed with the ability to separate to some extent the two classes of events, the detectors with an argon target shine in this particular area. When ionized, ultra-pure liquid argon emanates a large quantity of scintillation photons, separated in two different classes depending on the spin of the collection of argon atoms (short-lived proto-molecular associations or “dimers”). For peculiar reasons connected with the quantum properties of liquified noble gases, the distribution of scintillation photons among the triplet and singlet states of the scintillating dimers is strongly tied to the density of ionization. Argon is special among all noble gases because the decay time of the two different classes of dimers (singlet and triplet) differs by more than a factor 1000! As a consequence, unlike other noble gases, an argon-based detector offers the ability of discriminating against minimum ionizing events in favor of nuclear recoils at better than one part in 10 billions in the energy range of interest for Dark Matter searches.

Buoyed by this unique feature, argon seems indeed to be primed to play a special role in large-scale DM searches if not for a technical problem that seemed at first insurmountable.

Argon is produced very cheaply from the air (1% of volume, to be compared with 78% of nitrogen and 21% of oxygen) and available in large quantities, but argon from the atmosphere is polluted with significant amounts of a radioactive isotope produced in the out layers of the atmosphere, ³⁹Ar. The activity level of this isotope, though so low that it does not present problems for humankind and livestock and generally gets by unnoticed, is sufficient to create big trouble in DM land. At 1 kBq/tonne of material, ³⁹Ar activity would make any argon-based detector with 10 or more tonnes of target continuously flashing, negating de facto the possibility of recording pristine events from potential candidate DM interactions unimpeded by superimposed ³⁹Ar flashes.

How to exploit the benefits of argon without the interference of ³⁹Ar? An initial avenue was exploited in the middle of the 2000s by INFN in the course of the WARP program – the precursor of all argon-based DM experiments, which along DarkSide-50, DEAP-3600, and MiniCLEAN helped making a strong case for the interest in this technology. INFN procured a small initial batch of 2 kg of argon depleted in ³⁹Ar via the use of centrifuges in a Russian facility, opening the path towards a new era of depleted-argon detectors for DM searches. But at the same time, this experience clarified that both the cost and reduction factor offered by the isotopic separation for centrifugation were not sustainable in the long run, considering the need to move from detectors of a few kg to detectors of several tens of tonnes. The solution, as often happens in this field, came from underground.

With initial support from the U.S. National Science Foundation and the Canada Foundation for Innovation, a group of researchers from the U.S., Canada, and Italy mounted a campaign for the identification of underground sources of argon. The hypothesis was that, protected by the Earth overburden, argon gas in deep pockets could be subject to minimal activation by cosmic rays and be left with a reduced content in ³⁹Ar. The researchers found fertile ground in the region of the four corners, where the four states of New Mexico, Colorado, Utah, and Arizona meet. The spectacular pinnacles of red rock littering this land once roamed by the Navajos are the remnants of very ancient volcanoes. The entire region is characterized by a very thin crust, which allows the gas originating from the mantle to reach the level of 10000 feet from the surface. The researchers established that gas wells in this region contain a small but significant amount of argon. By collecting, purifying, and distilling 200 kg of argon into detector-grade gas, and by operating with this gas the DarkSide-50 detector in the underground LNGS, the researchers established that the abatement in ³⁹Ar is sufficiently strong (more than a factor 1000) and the cost for extraction and purification sufficiently contained to warrant construction of a large- scale facility to support the next-generation DM experiments. To fully exploit this argon source, INFN committed to construct the Urania plant for large-scale (300 kg/day) extraction of argon in the four corners region. As of October 2021, the plant is about to be completed and delivered in the U.S.

Thanks to the kindness of nature and the availability of underground argon suppressed in ³⁹Ar, a new generation of argon-based experiments, with target masses of several tens or hundreds of tonnes, are now made possible. The first experiment taking advantage of this argon bonanza will be DarkSide-20k, conceived, proposed, and designed by the “Global Argon Dark Matter Collaboration”, participated by 55 Institutes and Universities from 15 different countries, and involving more than 550 researchers (physicists, engineers and technicians). The collaboration is led by its Spokesperson, Cristiano Galbiati of Princeton University and Gran Sasso Science Institute, (GSSI), and by its Institutional Board Chair, Arthur McDonald of Queen’s University, Canada, the 2015 Nobel Laureate for Physics. With a capital cost of approximately 100 million Euros, the DarkSide-20k will be a flagship DM experiment for LNGS, where construction is about to start in the underground Hall C.

3 The ARIA project

Though Nature was kind in providing sources of underground argon with a strong abatement in ³⁹Ar, argon is such an important material for the next generation of DM experiments to leave the ultimate control on its radioactivity only to nature. Enter ARIA, the brainchild of Cristiano Galbiati, who proposed in 2015 to INFN the construction of a cryogenic distillation tower able to separate the isotopes of argon.

Cryogenic distillation is regularly used in industry for the production of stable light isotopes (¹³C, ¹⁵N, ¹⁸O) for advanced medical diagnostics. But the ratio of relative volatilities of heavier isotopes such as ³⁹Ar/⁴⁰Ar is so small that their efficient and cost-effective separation required a very special plant: a single, hundreds-of-meters tall cryogenic distillation column containing several thousands of equivalent plates. It was apparent from the beginning that the real problem would lie in the structure and stability of the column, much taller than anything previously built, not to mention conceived. At the root of the invention of ARIA is the realization that the effective construction of the column would require hosting it in a mine shaft, transferring the load of each element to the walls of the shaft. The realization that similar infrastructures existed in the Italian region most littered with mines, Sardinia, and the discovery of a suitable mine shaft in the “Monte Sinni” mine of Carbosulcis S.p.A. in Gonnesa (SU), marked the start of this ambitious project that will lead to the construction of the tallest plant in the world.

The innovative Aria project is part of this context, the primary objective of which is essential support for one of the most important basic research programs on DM, the DarkSide-20k experiment, an impressive upgrade of DarkSide-50 as it provides for the use of about 60 tonnes of argon-40 (20 tonnes of fiducial volume of the detector, a Time Projection Chamber with liquid argon) depleted of the radioactive isotope ³⁹Ar. Equipped with highly innovative reading electronics, silicon light sensors, this new detector will be able to extend the search for Dark Matter particles to masses that go beyond the exploration limit of the experimental equipment operating at current particle accelerators, including LHC at CERN in Geneva.

DarkSide-50, which has an effective mass of 50 kg, demonstrated the feasibility of the technique and the possibility of scaling the detector to much larger masses to increase its sensitivity. The argon used in DarkSide-50 was mined from underground CO₂ wells in Cortez, Colorado, via a pioneering chemical plant. The depletion factor of ³⁹Ar in this gas, compared to that of atmospheric argon, is greater than 1400. However, when the detector is scaled to a larger size, the residual ³⁹Ar increases, and it is therefore necessary to further purify the detector if one wants to carry out a zero-background experiment. Therefore, the strategy of the DarkSide-20k experiment is divided into two projects:

1. upgrade of the CO₂ extraction facility in Colorado. With the current extraction and first purification plant, 0.3-0.5 kg/day of underground argon are produced. A new plant, currently being defined, will produce around 250 kg/day, the Urania Project;

2. design and construction of an underground argon isotope separation plant to further reduce the ³⁹Ar content and separate other rare and stable isotopes with possible applications in other disciplinary fields, the ARIA Project.

ARIA provides for the installation of a cryogenic distillation tower for the production of stable isotopes enriched with very high purity. For this scope, the Aria column will need about 3000 distillation stages for a total height of around 350 m (more than the Eiffel tour).

All isotopes, both of scientific and commercial interest, are derived from air. The chosen technique, i.e. cryogenic distillation, is the most effective production method for the production of enriched stable isotopes.

The isotope separation by cryogenic distillation has as its basic physical principle the difference in volatility of the different isotopes that must be distilled. In the 1960s, measurements were made of the relationship between the vapor tensions between isotopes of the same element, including the ratio of the argon-36/argon-40 vapor tensions. In the same years the two scientists Fieschi and Terzi developed a model that predicts the relationship between vapor tensions between isotopes of the same element. The model was verified on the experimental data available and on the basis of this relationship it was possible to estimate that the number of theoretical steps necessary to reduce the argon-39 content by a factor of 10 is equal to over 2500. The process therefore requires the operation of a single column several hundred meters high to contain this high number of theoretical stages.

Therefore, analytical studies and detailed simulations have demonstrated the feasibility of the project and have highlighted the enormous potential of the column also on other isotopes of vast interest in medical diagnostics and beyond. For example, the column can carry out the isotope separation of the following chemical species:

• argon (Ar) for enrichment of ⁴⁰Ar,
• nitrogen (N₂) for enrichment of ¹⁵N,
• oxygen (O₂) for enrichment of ¹⁷O₂, ¹⁸O₂,
• carbon monoxide (CO) for enrichment of ¹³C, ¹⁷O₂, ¹⁸O₂,

and possibly of other species that could be considered of future interest. These isotopes find application in clinical studies for the production of tracers for Positron Emission Tomography (PET) anticancer diagnostics, of tracers of interest for clinical studies in general and of tracers of interest for environmental and agricultural sciences.

INFN and the Regione Autonoma della Sardegna (RAS) have signed a memorandum of understanding to develop the project described, aimed at creating an innovative research infrastructure at the Monte Sinni mine, in the Sulcis coal basin, in Sardinia. The mine is managed by Carbosulcis S.p.A. which had a plan for the closure (end of 2018) and partial conversion of the mine that has been implemented since January 2019. The memorandum of understanding has allowed the opening of a discussion table between INFN and RAS for the installation in the mine of a high-level technological plant, in correspondence with the wells of Seruci. The height and diameter of the wells, their configuration, with multiple accesses and integrated safety systems and, above all, the availability of a descendery (tunnel ramp accessible to large vehicles) from the surface up to a depth of 500 meters, are considered by INFN to be ideal conditions for a safe installation of a plant that will have unique dimensions in the world and would be the first in Europe.

ARIA’s first step therefore involves the installation of a cryogenic distillation pilot tower. With a diameter of about 30 cm and a length of about 26 m, it is the so-called Seruci-0 column. This project, unprecedented at an international level, is made possible by the cooperation between INFN, with the role of guide and coordination of the research groups involved, and Princeton University, as well as by the crucial contribution of Italian companies in the most industrial phase.

The ARIA project is an important example of how basic research can offer the opportunity for a potential industrial exploitation of the techniques developed for experiments at the frontier of knowledge. It is a project on which the RAS has been working for months in agreement with INFN (and Princeton University as well as supplier) as it recognizes one of the opportunities to renew the role of Sardinia and its economic activities. The goal is that, in the presence of good results, it can follow the industrial “scalability” of the project, in consideration of the excellent market prospects and technological development linked to the use of possible products. Sardinia, in addition to the precise infrastructural needs linked to the realization of the project, has proposed itself as a reliable partner thanks to the accurate choice of focusing on research and innovation, the high level of qualification of the workers who may be involved and the availability of excellence coming from Sardinian universities. The initiative is an excellent example of how even critical sectors such as the one in which Carbosulcis operates, can find new directions and potential thanks to the skills acquired, the technologies developed and the contribution of new research. The technological skills of its engineers and mining technicians are of the highest level: it would have been impossible to arrive at the feasibility study of this project without their decisive contribution.

The ARIA project, therefore, as well as being of fundamental importance for basic research and at the service of advanced experimentation that takes place at the Gran Sasso National Laboratories for the search of Dark Matter, is also of considerable regional and national strategic importance and of high interest in the possible local repercussions that the activities carried out could entail. The spin-off of this technology could allow an important impact on a social level, of the companies on the territory and of the research centers of the Sardinia Region, starting from the University. Sectors that would benefit from it range from diagnostic medicine, with particular reference to advanced screening for various diseases, clean energy, eco-sustainability, agriculture, and the study of climate change. In short, a new production cycle with a very high technical content could be established, with potential repercussions on local employment.

The project consists of a first development aimed at research through a pilot plant built with the final technology whose operation is preparatory to the phase of industrial exploitation.

4 Technical description

4.1 Process description

Figure 1 shows the P&ID of the system. The cryogenic column, the exchangers and the various pipes are contained within the so-called cold box, kept under vacuum (around 10^–5 mbar), the purpose of which is to minimize heat losses with the environment. To minimize even the heat losses related to radiation, a common and consolidated technique is used in technologically advanced applications such as the installation of some layers of a special super-insulating material. The system consists of three independent circuits:

1. process circuit;
2. refrigeration (or auxiliary for cooling) circuit;
3. vacuum system.

The power supply of the so-called process column is controlled with a PID regulation between flowmeters and valves. The column is filled with structured packing to increase the exchange surface between liquid and gaseous phase and to increase the heat exchange mass. At the top of the column, a heat-exchanger, the so-called “condenser”, is fed with the refrigerant fluid, liquid nitrogen (LN₂) (or krypton depending on the specific separation process in progress). The liquid condensed is used as reflux in the distillation column. Another heat-exchanger, the so-called “reboiler”, placed at the bottom of the column, is also powered by the refrigerant fluid through the refrigerant fluid recirculation compressor. The isotopes with lower volatility extracted from the bottom of the column in liquid phase are then gasified and conveyed to the storage/treatment plant. Likewise, the mixture of more volatile isotopes collected at the top is gasified, and conveyed to the product storage/treatment plant. To optimize energy consumption, the refrigerant fluid is processed in a closed circuit by the refrigerant gas compressor: the compressed gas is cooled in an exchanger, liquefied in the reboiler and then sent, via a liquid cryogenic pump, to the top of the column. Only a small fraction of heat is lost and compensated by external contributions to keep the thermal equilibrium of the system balanced.

4.2 Process and design parameters

In the first phase (or phase 0) of the project, the plant will be used to validate the simulations with argon. Before these tests, the plant was commissioned with nitrogen. The results of this operation will be discussed and detailed later.

The column is made up of 28 identical central modules, 12 m in height and 0.71 m in diameter, and a bottom module (reboiler), 4 meters in height and 1.5 m in diameter, and a head module (condenser), 9 meters in height and 1.2 meter in diameter. The modules will be welded together on site using orbital welds, and all connections inside the cold box will be performed with orbital welds and will be verified by radiographic tests (X-rays). Moreover, after the construction, the column will be completely checked by a leak test method with an acceptance rate of 10^–9 mbar L/s. It is worth highlighting that all the modules are also checked and approved with the same rate of acceptance in two steps: one directly performed by the Aria group to the production site and the second one, at CERN by the CERN colleagues as part of the KN3155/TE service agreement. In order to absorb the thermal excursions, between each central module a proper bellows (also checked at CERN) will be installed.

4.3 Support structure

Figure 2 shows an air overview of the Seruci mine infrastructure and one of the first platforms that will support the column installed in the shaft. The column will occupy the left half of the well while the “cage”, or the lift moved by the winch located outside the well, which allows the transport and handling of personnel and materials, will occupy the right half.

The support platforms will be arranged along the entire height of the well at a distance of 4 m from each other. Each platform will be equipped with an access ladder that will connect it with the adjacent ones. The column modules will be equipped with special anchoring systems to the corresponding platforms. The structure was optimized to be able to accommodate, possibly at a later time, a larger column for the large-scale production of stable isotopes.

4.4 Auxiliary systems

For the overall operation of the process, other auxiliary equipment/systems are required which may differ with the element treated in the column. The picture reported in fig. 3 shows the auxiliary equipment installed in the Seruci-0 plant.

The refrigerant fluid is stored in a cryogenic liquid tank equipped with a vaporizer for the use of nitrogen in the gas phase necessary for the process or for other uses. Gaseous nitrogen, for example, can be used as a back-up in case of compressor malfunction or power failure to keep the system running for a certain period. The gas to be treated is introduced into the process circuit from compressed gas cylinders (or from customized cryogenic liquid tank for the Underground Ar (Uar) for the Seruci-1 phase) through a power supply adjustment unit, including a pressure reducer, a buffer tank and a safety device.

The distilled product and the bottom product, after leaving the distillation column, are transferred into compressed gas cylinders by means of compressors. For the Seruci-1 phase the UAr produced will be stored again into the cryogenic liquid tank. The product storage system, both gas or liquid, will be positioned at ground level, in an area outside the well and equipped with a suitable base and appropriate cover. Since in the cases mentioned above also the distillate, which represents the waste of the isotope separation, has a commercial value, it will be recovered and consequently there will be no emissions into the environment.

5 Seruci-0 operations

Since July 2019 the plant was commissioned with nitrogen in both the refrigeration and distillation circuits. The commissioning was divided in 4 runs, which involved DS Collaboration members coming from different countries, such as Italy (specifically from INFN Cagliari Section, University of Cagliari, Gran Sasso National Laboratory and Gran Sasso Science Institute), Poland, Romania, Spain and USA. During the runs, a quadrupole mass spectrometer was used to measure the fluid composition, at the reboiler, condenser, and feed line. The results of the distillation run confirmed the expectations based on theory.

These results confirmed the capacity of the plant to perform the isotopic distillation.

6 Conclusions

As in a perfect puzzle, the needs of the international scientific world have found total correspondence in the characteristics of the mining site managed by Carbosulcis, creating the right conditions and the necessary premises for the ARIA project. The INFN has seen the possibility of realizing the apparatus capable of producing the depleted argon necessary for the DarkSide experiment, in a site particularly suitable from the technical and logistical point of view, both for the availability of a well of the right size, and for the presence of specialized personnel. On the other hand, the RAS has identified in the project an incredible opportunity, to proceed to a reconversion of the mining complex, just in a historical moment in which the extraction of coal as fuel for power plants has come to an end. Precisely for this reason, the Aria project is extremely important not only for Carbosulcis, but also for the potential impact on companies operating in the region, both in terms of increased employment and for the related training activities in the fields of chemical engineering, process engineering, environmental engineering, cryogenic mechanics and particle physics, thus promoting the regional system of scientific research and the dissemination of scientific and technological culture in a broad international context. Since the first steps of the ARIA project, which date back to 2015, Carbosulcis has guaranteed collaboration in all phases by ensuring the expertise and availability of experienced technicians and engineers. Finally, in the agreements reached with the RAS, the necessary funds were also requested in order to be able to finance contracts for job positions of primary importance in the staff needed to manage the plant.

Moreover, the Aria project provide a further opportunity for the territory. The Carbosulcis mine, in fact, extracts about three thousand cubic meters of water per day to ensure the operation of the mine by avoiding flooding. This water has a temperature of about 40 °C and its calorific value is released into the environment, because the associated enthalpy rise is limited and insufficient for industrial use. Hence another idea of Cristiano Galbiati came into being, in collaboration with the University of Cagliari, to develop the project “Spirulina del Sulcis”, for the experimentation of the cultivation of spirulina, thanks to the use of innovative technologies and natural and renewable energy sources. Spirulina is a microalga whose use as an organic “superfood” in the food sector, but also in cosmetics and pharmaceuticals, is strongly growing. In particular, the use of mine water as an energy carrier for the continuous heating of crops allows to maintain optimal conditions for the growth of the culture throughout the year, doubling the production period of about 6 months compared to conventional plants. An innovative, patented anaerobic photobioreactor has already been built in Carbosulcis premises, allowing the growth of spirulina and other microalgae under controlled conditions.

In addition to the cultivation of spirulina in dedicated areas on the surface of Carbosulcis, the future possibility of producing spirulina marked with carbon-13 offers concrete possibilities of growth and development for the territory, also in the field of molecular biology. It may be useful to remember that carbon-13, one of the two stable isotopes of carbon (the other stable isotope is carbon-12) in nature, represents about 1% of the element. The importance of carbon-13 is related to its use as a tracer to follow the carbon atoms in chemical and biochemical processes using compounds suitably enriched with this isotope.

In conclusion, the Aria project, of fundamental importance for the research on Dark Matter, has the right potential to be extremely useful and versatile for distillation plants able to produce isotopes to be used in different areas, such as diagnostic medicine, clean energy, agriculture and create real development opportunities for the territory.

Acknowledgments

The second phase of the leak checks, carried out at CERN, was performed under service agreement KN3155/ TE. We acknowledge the professional contribution of the Mine and Electrical Maintenance staff of Carbosulcis S.p.A. Part of the project funding comes from Intervento finanziato con risorse FSC 2014-2020 - Patto per lo Sviluppo della Regione Sardegna. This paper is based upon work supported by the U.S. National Science Foundation (NSF) (Grants No. PHY-0919363, No. PHY-1004054, No. PHY-1004072, No. PHY-1242585, No. PHY-1314483, No. PHY- 1314507, associated collaborative grants, No. PHY-1211308, No. PHY-1314501, No. PHY-1455351 and No. PHY-1606912, as well as Major Research Instrumentation Grant No. MRI-1429544), the Italian Istituto Nazionale di Fisica Nucleare (Grants from Italian Ministero dell’Istruzione, Università, e Ricerca ARIA e la Ricerca della Materia Oscura - Fondo Integrativo Speciale per la Ricerca (FISR) and Progetto Premiale 2013 and Commissione Scientifica Nazionale II). We acknowledge the financial support by LabEx UnivEarthS (ANR-10-LABX-0023 and ANR-18-IDEX-0001), the Natural Sciences and Engineering Research Council of Canada, SNOLAB, Arthur B. McDonald Canadian Astroparticle Physics Research Institute, and the São Paulo Research Foundation (Grant No. FAPESP - 2017/26238-4). The authors were also supported by the Unidad de Excelencia María de Maeztu:
CIEMAT-Física de partículas (Grant No. MDM 2015-0509), the Polish National Science Centre (Grant No. UMO- 2019/33/B/- ST2/02884), the Foundation for Polish Science (Grant No. TEAM/2016 - 2/17), the International Research Agenda Program AstroCeNT (Grant No. MAB/2018/7) funded by the Foundation for Polish Science from the European Regional Development Fund, the European Union’s Horizon 2020 research and innovation program under grant agreement No 962480, the Science and Technology Facilities Council, part of the United Kingdom Research and Innovation, and The Royal Society (United Kingdom). I.F.M.A is supported in part by Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq). We also wish to acknowledge the support from Pacific Northwest National Laboratory, which is operated by Battelle for the U.S. Department of Energy under Contract No. DE-AC05-76RL01830.