CUORE Underground Experiment in Italy Carries on Despite Pandemic

Tuesday, May 12, 2020

Press release from LBNL

As the COVID-19 outbreak took hold in Italy, researchers working on a nuclear physics experiment called CUORE at an underground laboratory in central Italy scrambled to keep the ultrasensitive experiment running and launch new tools and rules for remote operations.

This Cryogenic Underground Observatory for Rare Events experiment – designed to find a never-before-seen process involving ghostly particles known as neutrinos, to explain why matter won out over antimatter in our universe, and to also hunt for signs of mysterious dark matter – is carrying on with its data-taking uninterrupted while some other projects and experiments around the globe have been put on hold.

Finding evidence for these rare processes requires long periods of data collection – and a lot of patience. CUORE has been collecting data since May 2017, and after upgrade efforts in 2018 and 2019 the experiment has been running continuously.

Before the pandemic hit there were already tools in place that stabilized the extreme cooling required for CUORE’s detectors and provided some remote controls and monitoring of CUORE systems, noted Yury Kolomensky, senior faculty scientist at the U.S. Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) and the U.S. spokesperson for CUORE.

The rapid global spread of the disease, and related restrictions on access to the CUORE experiment at Gran Sasso National Laboratory (Laboratori Nazionali del Gran Sasso, or LNGS, operated by the Italian Nuclear Physics Institute, INFN) in central Italy, prompted CUORE leadership and researchers – working in three continents – to act quickly to ramp up the remote controls to prepare for an extended period with only limited access to the experiment.

Just days before the new restrictions went into effect at Gran Sasso, CUORE leadership on March 4 made the decision to rapidly deploy a new remote system and to work out the details of how to best maintain the experiment with limited staffing and with researchers monitoring in different time zones. The new system was fully operational about a week later, and researchers at Berkeley Lab played a role in rolling it out.

“We were already planning to transition to remote shift operations, whereby a scientist at a home institution would monitor the systems in real time, respond to alarms, and call on-site and on-call personnel in case an emergency intervention is needed,” Kolomensky said, adding, “We were commissioning the system at the time of the outbreak.”

Brad Welliver, a postdoctoral researcher, served as Berkeley Lab’s lead developer for the new remote monitoring system, and Berkeley Lab staff scientist Brian Fujikawa was the overall project lead for the enhanced remote controls, collectively known as CORC, for CUORE Online/Offline Run Check.

Fujikawa tested controls for starting and stopping the data collection process, and also performed other electronics testing for the experiment from his home in the San Francisco Bay Area.

He noted that the system is programmed to send email and voice alarms to the designated on-shift CUORE researcher if something is awry with any CUORE system. “This alarm system is particularly important when operating CUORE remotely,” he said, as in some cases on-site workers may need to visit the experiment promptly to perform repairs or other needed work.

Development of so-called “slow controls,” which allow researchers to monitor and control CUORE equipment such as pumps and sensors, was led by Joe Johnston at the Massachusetts Institute of Technology.

“Now we can perform most of the operations from 6,000 miles away,” Kolomensky said.

And many participants across the collaboration continue to play meaningful roles in the experiment from their homes, from analyzing data and writing papers to participating in long-term planning and remote meetings.

Despite access restrictions at Gran Sasso, experiments are still accessible for necessary work and checkups. The laboratory remains open in a limited way, and its staff still maintains all of its needed services and equipment, from shuttles to computing services.

Laura Marini, a postdoctoral researcher at UC Berkeley who serves as a run coordinator for CUORE and is now living near Gran Sasso, is among a handful of CUORE researchers who still routinely visits the lab site.

“As a run coordinator, I need to make sure that the experiment works fine and the data quality is good,” she said. “Before the pandemic spread, I was going underground maybe not every day, but at least a few times a week.” Now, it can be about once every two weeks.

Sometimes she is there to carry out simple fixes, like a stuck computer that needs to be restarted, she said. Now, in addition to the requisite hard hat and heavy shoes, Marini – like so many others around the globe who are continuing to work – must wear a mask and gloves to guard against the spread of COVID-19.

The simple act of driving into the lab site can be complicated, too, she said. “The other day, I had to go underground and the police stopped me. So I had to fill in a paper to declare why I was going underground, the fact that it was needed, and that I was not just wandering around by car,” she said. Restrictions in Italy prevent most types of travel.

CUORE researchers note that they are fortunate the experiment was already in a state of steady data-taking when the pandemic hit. “There is no need for continuous intervention,” Marini said. “We can do most of our checks by remote.”

She said she is grateful to be part of an international team that has “worked together on a common goal and continues to do so” despite the present-day challenges.

Kolomensky noted some of the regular maintenance and upgrades planned for CUORE will be put off as a result of the shelter-in-place restrictions, though there also appears to be an odd benefit of the reduced activity at the Gran Sasso site. “We see an overall reduction in the detector noise, which we attribute to a significantly lower level of activity at the underground lab and less traffic in the highway tunnel,” he said. Researchers are working to verify this.

CUORE already had systems in place to individually and remotely monitor data-taking by each of the experiment’s 988 detectors. Benjamin Schmidt, a Berkeley Lab postdoctoral researcher, had even developed software that automatically flags periods of “noisy” or poor data-taking captured by CUORE’s array of detectors.

Kolomensky noted that work on the CORC remote tools is continuing. “As we have gained more experience and discovered issues, improvements and bug fixes have been implemented, and these efforts are still ongoing,” he said.

CUORE is supported by the U.S. Department of Energy Office of Science, Italy’s National Institute of Nuclear Physics (Instituto Nazionale di Fisica Nucleare, or INFN), and the National Science Foundation (NSF). CUORE collaboration members include: INFN, University of Bologna, University of Genoa, University of Milano-Bicocca, and Sapienza University in Italy; California Polytechnic State University, San Luis Obispo; Berkeley Lab; Lawrence Livermore National Laboratory; Massachusetts Institute of Technology; University of California, Berkeley; University of California, Los Angeles; University of South Carolina; Virginia Polytechnic Institute and State University; and Yale University in the US; Saclay Nuclear Research Center (CEA) and the Irène Joliot-Curie Laboratory (CNRS/IN2P3, Paris Saclay University) in France; and Fudan University and Shanghai Jiao Tong University in China.

The CUORE Underground Experiment Narrows the Search for Rare Particle Process

Thursday, January 9, 2020

Press release from LBNL

In an underground laboratory deep beneath a mountain in Central Italy, an array of crystals, chilled to within a hair of absolute zero – the coldest possible temperature in the universe – has been steadily compiling one of the most precise measurements to date in pursuit of a rare particle process. If it is proven to exist, this process may well be the “smoking gun” of how matter was created in the universe.

The experiment that is designed to seek out this process, called CUORE (Cryogenic Underground Observatory for Rare Events), is at Gran Sasso National Laboratories, part of the Italian National Institute for Nuclear Physics (INFN).

The observation of this process, known as neutrinoless double-beta decay, would have profound implications for understanding the properties of ghostly, abundant particles called neutrinos that pass through most matter unaffected. U.S. Department of Energy-supported nuclear physicists play a leading scientific and technical role in this experiment.

The latest results represent more than a 2-year span of data collection – from April 2017 to July 2019. This dataset, which is about four times larger than the initial results announced in October 2017 (see a related article), sets even more stringent limits on the theoretical ultra-rare process that CUORE is designed to seek out.

The CUORE detector is surrounded by a layer of highly pure lead that was recovered from a 2,000-year-old Roman shipwreck. (Credit: CUORE Collaboration)

Double-beta decay is a proven particle process in which two neutrons, which are uncharged particles in an atom’s nucleus, morph into two protons and emit two electrons and two antineutrinos. Antineutrinos are the antiparticles, or antimatter counterparts, to neutrinos.

CUORE is designed to detect the signature of a theoretical neutrinoless double-beta decay process in which no antineutrinos are created. This is because they would erase each other in the decay process, proving that the neutrino is its own antiparticle, as the Italian scientist Ettore Majorana hypothesized in 1937.

“We have now more than quadrupled the collected data, reaching one of the best sensitivities worldwide for the discovery of this rare particle process,” said Oliviero Cremonesi, senior researcher at INFN Milano Bicocca and spokesperson of the CUORE Collaboration.

Yury Kolomensky, U.S. spokesperson for the CUORE collaboration and senior faculty scientist at the U.S. Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab), said, “The decay process in the CUORE crystals is a matter-creating process relevant to the Big Bang at the inception of our universe, and could help us to explain how matter won out over antimatter in its evolution.” Kolomensky is also a physics professor at UC Berkeley.

Discovery of this neutrinoless process would mean that a neutrino and an antineutrino, which are both electrically neutral, are essentially the same particle (called a Majorana neutrino) and only differ in a mirroring property known as helicity. Helicity is somewhat analogous to a person being either left-handed or right-handed, and a Majorana neutrino could switch handedness – akin to an ambidextrous person.

The CUORE detector array consists of 988 cube-shaped crystals made of a highly purified, natural form of tellurium dioxide that are stacked in 19 copper-cladded towers.

The CUORE detector array during assembly. (Credit: Yura Suvorov)

While no sign of neutrinoless double-beta decay is found in the data at this time, CUORE improved by a factor of two, compared to the previous results, the bound on the rate of this process in the nuclei of tellurium-130 atoms that are contained in the CUORE crystals. The interpretation of this result is a tighter bound on the allowed value of the neutrino mass in the Majorana hypothesis, which now extends below one-tenth of an electronvolt, at least 5 million times lighter than an electron.

The results incorporate a sophisticated new algorithm that helps to amplify CUORE’s detected signals while cutting out unwanted background “noise.” The algorithm helps identify and reject signals caused by small energy deposits in the detectors, such as those left by some other, well-known particle decays. This could provide a cleaner signature of neutrinoless double-beta decay.

The new algorithm would also allow CUORE to hunt for theoretical particles of dark matter known as WIMPs, or weakly interacting massive particles, in its nearly 1-ton detector.

“This is the largest, most sensitive detector of its kind in the world,” said Thomas O’Donnell, professor of physics at Virginia Tech University and a member of the CUORE Physics Board that organized and coordinated the data analysis. “Each month we are accumulating as much data as some detectors get in a year.”
CUORE detector rendering

An illustration of the cross-section of the CUORE experiment with a human figure for scale. The chambers encasing the central detector are used to deeply chill the detector. (Credit: CUORE Collaboration)

CUORE’s latest results represent the largest dataset collected by a particle detector that uses solid crystals, rather than the more common tank of liquid, in an effort to find this particle process. It is the first example of a solid-state detector with nearly a ton of mass.

Solid-state detectors have the ability to very accurately measure the energy of particle decays. But it is challenging to scale up a solid-state detector to very large sizes when compared to a liquid-based detector.

“We are delighted that we are now operating the detectors at close to 90% efficiency,” added Carlo Bucci, senior researcher at INFN’s Gran Sasso, who is the Italian spokesperson and technical coordinator of the experiment. “All of the work invested in the last two years to bring the system to this performance has paid off. Warming up and cooling back down takes several months, so we have to get it right each time.”

The crystal array is extremely sensitive to a very slight and narrow energy signature that is predicted for the neutrinoless decay process. Chilling the array to below minus 459 degrees Fahrenheit makes the entire array, which weighs about 1,650 pounds, sensitive to an incredibly slight rise in temperature arising from a particle interaction with a detector crystal. The tellurium-130 in the crystals, which is the decaying component in the detector, accounts for about 450 pounds of that weight.

This heightened sensitivity, which enables CUORE to look for signatures of dark matter particles – could possibly help to understand a periodic signal that a dark matter experiment called DAMA/LIBRA, installed at the same Gran Sasso site, has reported.

After CUORE’s 5-year run, a planned next-gen upgrade called CUPID will exchange the tellurium crystals with new crystals that will use a form of molybdenum with light-emitting properties. These crystals can produce both temperature-based and light-based signals that will further extend the sensitivity of the detector’s measurements.

“It is an exciting time for neutrino physics,” said Claudia Tomei, a member of the CUORE Executive Board and a researcher at INFN Roma, “with numerous complementary experiments that will help us better understand the properties of neutrinos.”

Cremonesi added, “We know we’ll learn something. We’re aiming for definitive measurements.”

CUORE is supported by the U.S. Department of Energy, Italy’s National Institute of Nuclear Physics (Instituto Nazionale di Fisica Nucleare, or INFN), and the National Science Foundation (NSF). CUORE collaboration members include: INFN, University of Bologna, University of Genoa, University of Milano-Bicocca, and Sapienza University in Italy; California Polytechnic State University, San Luis Obispo; Berkeley Lab; Lawrence Livermore National Laboratory; Massachusetts Institute of Technology; University of California, Berkeley; University of California, Los Angeles; University of South Carolina; Virginia Polytechnic Institute and State University; and Yale University in the US; Saclay Nuclear Research Center (CEA) and the Irène Joliot-Curie Laboratory (CNRS/IN2P3, Paris Saclay University) in France; and Fudan University and Shanghai Jiao Tong University in China.

CUORE Provides Deeper Look into the Nature of Neutrinos

Monday, October 23, 2017

Press release from INFN

The first glimpse of data from the full array of a deeply chilled particle detector operating beneath a mountain in Italy sets the most precise limits yet on where scientists might find a theorized process to help explain why there is more matter than antimatter in the universe. This new result, submitted today to the journal Physical Review Letters, is based on two months of data collected from the full detector of the CUORE (Cryogenic Underground Observatory for Rare Events) experiment at the Italian National Institute for Nuclear Physics’ (INFN’s) Gran Sasso National Laboratories (LNGS) in Italy. CUORE means “heart” in Italian.

CUORE is considered one of the most promising efforts to determine whether tiny elementary particles called neutrinos, which interact only rarely with matter, are “Majorana particles” – identical to their own antiparticles. Most other particles are known to have antiparticles that have the same mass but a different charge, for example. CUORE could also help us home in on the exact masses of the three types, or “flavors,” of neutrinos – neutrinos have the unusual ability to morph into different forms.

“This is the first preview of what an instrument this size is able to do,” said Oliviero Cremonesi, a senior faculty scientist at INFN and spokesperson for the CUORE collaboration. Already, the full detector array’s sensitivity has exceeded the precision of the measurements reported in April 2015 after a successful two-year test run that enlisted one detector tower. Over the next five years CUORE will collect about 100 times more data.

Yury Kolomensky, a senior faculty scientist in the Nuclear Science Division at Lawrence Berkeley National Laboratory (Berkeley Lab) and U.S. spokesperson for the CUORE collaboration, said, “The detector is working exceptionally well and these two months of data are enough to exceed the previous limits.” Kolomensky is also a professor in the UC Berkeley Physics Department.

The new data provide a narrow range in which scientists might expect to see any indication of the particle process it is designed to find, known as neutrinoless double beta decay.

“CUORE is, in essence, one of the world’s most sensitive thermometers,” said Carlo Bucci, technical coordinator of the experiment and Italian spokesperson for the CUORE collaboration. Its detectors, formed by 19 copper-framed “towers” that each house a matrix of 52 cube-shaped, highly purified tellurium dioxide crystals, are suspended within the innermost chamber of six nested tanks.

Cooled by the most powerful refrigerator of its kind, the tanks subject the detector to the coldest known temperature recorded in a cubic meter volume in the entire universe: minus 459 degrees Fahrenheit (10 milliKelvin).

The detector array was designed and assembled over a 10-year period. It is shielded from many outside particles, such as cosmic rays that constantly bombard the Earth, by the 1,400 meters of rock above it, and by thick lead shielding that includes a radiation-depleted form of lead rescued from an ancient Roman shipwreck. Other detector materials were also prepared in ultrapure conditions, and the detectors were assembled in nitrogen-filled, sealed glove boxes to prevent contamination from regular air.

“Designing, building, and operating CUORE has been a long journey and a fantastic achievement,” said Ettore Fiorini, an Italian physicist who developed the concept of CUORE’s heat-sensitive detectors (tellurium dioxide bolometers), and the spokesperson-emeritus of the CUORE collaboration. “Employing thermal detectors to study neutrinos took several decades and brought to the development of technologies that can now be applied in many fields of research.”

Together weighing over 1,600 pounds, CUORE’s matrix of roughly fist-sized crystals is extremely sensitive to particle processes, especially at this extreme temperature. Associated instruments can precisely measure ever-slight temperature changes in the crystals resulting from these processes. The measurements carry the telltale signature of specific types of particle interactions or particle decays – a spontaneous process by which a particle or particles transform into other particles.

In double beta decay, which has been observed in previous experiments, two neutrons in the atomic nucleus of a radioactive element become two protons. Also, two electrons are emitted, along with two other particles called antineutrinos.

Neutrinoless double beta decay, meanwhile – the specific process that CUORE is designed to find or to rule out – would not produce any antineutrinos. This would mean that neutrinos are their own antiparticles. During this decay process the two antineutrino particles would effectively wipe each other out, leaving no trace in the CUORE detector. Evidence for this type of decay process would also help scientists explain neutrinos’ role in the imbalance of matter vs. antimatter in our universe.

Neutrinoless double beta decay is expected to be exceedingly rare, occurring at most (if at all) once every 100 septillion (1 followed by 26 zeros) years in a given atom’s nucleus. The large volume of detector crystals is intended to greatly increase the likelihood of recording such an event during the lifetime of the experiment.

There is growing competition from new and planned experiments to resolve whether this process exists using a variety of search techniques, and Kolomensky noted, “The competition always helps. It drives progress, and also we can verify each other’s results, and help each other with materials screening and data analysis techniques.”

Lindley Winslow of the Massachusetts Institute of Technology, who coordinated the analysis of the CUORE data, said, “We are tantalizing close to completely unexplored territory and there is great possibility for discovery. It is an exciting time to be on the experiment.”

CUORE is supported jointly by the Italian National Institute for Nuclear Physics Istituto Nazionale di Fisica Nucleare (INFN) in Italy, and the U.S. Department of Energy’s Office of Nuclear Physics, the National Science Foundation, and the Alfred P. Sloan Foundation in the U.S. The CORE collaboration includes about 150 scientists from Italy, U.S., China, France, and Spain, and is based in the underground Italian facility called INFN Gran Sasso National Laboratories (LNGS) of the INFN. Berkeley Lab leads the U.S. nuclear physics effort for the international CUORE collaboration.

CUORE collaboration members include: Italian National Institute for Nuclear Physics (INFN), University of Bologna, University of Genoa, University of Milano-Bicocca, and Sapienza University in Italy; California Polytechnic State University, San Luis Obispo; Berkeley Lab; Lawrence Livermore National Laboratory; Massachusetts Institute of Technology; University of California, Berkeley; University of California, Los Angeles; University of South Carolina; Virginia Polytechnic Institute and State University; and Yale University in the US; Saclay Nuclear Research Center (CEA) and the Center for Nuclear Science and Materials Science (CNRS/IN2P3) in France; and the Shanghai Institute of Applied Physics and Shanghai Jiao Tong University in China.

CUORE has reached its operating temperature

Monday, January 30, 2017

We're very excited to announce a new milestone for our experiment: the CUORE detector has reached its operating temperature of 10 mK! This is over one ton of tellurium dioxide and copper cooled to a hundredth of a degree above absolute zero. We are now seeing clear signals from the detector, and our next phase is the optimization of our electronics and analysis software. Soon, we will begin taking official data, so stay tuned!

Thank you to all CUORE Collaborators, past and present, who have helped us reach this milestone!

Detector Installation Completed

Thursday, September 1, 2016

The CUORE experiment, located at the Gran Sasso National Laboratories (LNGS) of the National Institute of Nuclear Physics (INFN) in Italy, has completed the installation of 19 "towers" that make up the detector. The delicate and precise operation, which required dedicated efforts of specially trained teams of scientists, engineers, and technicians, and logistical support from the entire collaboration, was completed on August 26.

"All of the 19 towers that make up the detector, consisting of 988 Tellurium oxide crystals and weighing nearly 750 kg (1650 lbs), are now suspended from the coldest point of the experiment cryostat," said Oliviero Cremonesi, the experiment’s spokesperson. "Now the collaboration is preparing for the finishing touches to the system, and will then proceed in the coming months with the closure of the cryostat, the cooldown, and the start of science operations."

CUORE is an experiment designed to study the properties of neutrinos. In particular, the experiment looks for a rare phenomenon called neutrinoless double beta decay. Revealing this process would demonstrate a Majorana nature of neutrinos, providing a possible explanation for the prevalence of matter over antimatter in the universe. The experiment is an international collaboration of about 165 scientists from thirty institutions in Italy, USA, China, and France. CUORE is supported jointly by the Italian National Institute for Nuclear Physics (INFN) and the Department of Energy’s Office of Science and National Science Foundation in the US.