The Cryogenic Underground Observatory for Rare Events’ site manager and operational coordinator is physicist Laura Marini (CUORE). The experiment is run by an international team and is located at the Gran Sasso National Laboratory of the National Institute of Nuclear Physics in the Italian region of Abruzzo. Marini completed a postdoctoral fellowship at the University of California, Berkeley after earning a PhD in physics from the University of Genoa in 2018. She started working on CUORE while pursuing her PhD, and she is currently connected to the Gran Sasso Science Institute and Gran Sasso lab in Italy. The recent milestone in the experiment’s ongoing investigation into whether neutrinos are Majorana particles was discussed by Marini with Richard Blaustein.
Can you describe your dual role at CUORE?
I currently manage CUORE’s site and serve as the experiment’s run coordinator. As run coordinator, I ensure that the experiment proceeds as planned. This is crucial because we want to collect data continuously for as long as possible because we are searching for extremely rare events. I am involved in both the data collection and the cryogenic portions of the experiment. I also work to reduce the amount of background noise in the experiment, which is crucial when searching for rare events. My site manager responsibilities go beyond those of a run coordinator. I coordinate on-site activities, manage the interface between the experiment and Gran Sasso National Laboratory, and plan the upkeep of all the systems and subsystems.
Can you explain CUORE and the things it aims to gauge?
CUORE was created specifically to look for neutrinoless double beta decay and searches for rare events in physics. If neutrinos are Majorana particles, or their own anti-particles, then this process is predicted to take place. It is crucial to provide a response to this query because, if neutrinos are shown to be Majorana particles, the puzzle of why neutrino masses are so small in the context of the Standard Model of particle physics will be cleared up. Tellurium-130 is known to undergo regular double beta decay and has a high natural abundance, so we look for neutrinoless double beta decay in this isotope. In a sizable cryostat, 184 tellurium dioxide crystals from CUORE are maintained at a temperature of about 10 mK. Instead of using liquid helium, the cryostat has five pulse tube cryocoolers. We search for neutrinoless double beta decay by measuring the minute temperature increase that results from the decay inside a crystal, so the experiment must be kept at a very low temperature. Prior to CUORE, only a small experimental volume and mass could be cooled; however, by cooling up to 1.5 tonnes of material at base temperature, we have greatly increased this capability. Another benefit of CUORE is that it operates over a wide energy range with excellent energy resolution, which should aid in identifying decay events.
What does CUORE’s recent accomplishment of collecting a “tonne-year” of data mean?
The term “tonne-year” refers to the mass of the tellurium oxide under observation times the duration of the experiment’s data collection. Data were gathered during runs carried out between 2017 and 2020, and the mass is 741 kg. Not every run used the entire mass, but overall data equivalent to one tonne-year were gathered. This has two important components. First off, a mass this size has never been cooled in a cryostat before. Second, we have demonstrated the viability of using cryogenic calorimeters to look for neutrinoless double beta decay because we were able to run the experiment for such a long time.
What did you and your colleagues learn from this ton-year of data?
To be clear, no Majorana particles have been discovered. The half-life of neutrinoless double beta decay has instead been given a lower limit. The half-life is now known to be longer than 2.21025 years. Because if the half-life was shorter, we would have anticipated seeing at least one or more events in CUORE, we can draw this conclusion.
Can CUORE be used to investigate different physics fields?
Yes. CUORE has the potential to look for dark matter because it is built to look for rare events. Rare interactions between dark matter particles and CUORE’s detector materials are predicted to release very small amounts of energy. Therefore, the experiment’s large mass and lengthy runtime would be advantageous in the search for dark matter. There are teams of physicists working on the CUORE collaboration who are considering the possibility of a dark matter search, which would entail examining an additional energy region in the detector.
Is there any connection between quantum computing and CUORE’s cryogenic milestone?
Although I am not an expert in quantum computing, solid state devices typically need long quantum coherence times to process quantum information. We are aware that both heat and cosmic rays shorten quantum coherence times. Advanced cryogenics can be used to conduct experiments underground, protecting against these harmful effects. Even though CUORE’s tellurium dioxide crystals can’t be used for quantum computing, the fact that we were able to conduct such a protracted experiment underground with a massive cryostat and clean materials may prove to be very beneficial for the advancement of quantum technologies.
What will the CUORE collaboration’s future hold?
The CUORE Upgrade with Particle Identification, or CUPID, which will replace CUORE once it expires in 2024, is already under development. We will switch the tellurium dioxide crystals in CUORE for lithium molybdate crystals. Heat and light are produced when particles from neutrinoless double beta decay collide with lithium molybdate. The ratio of heat to light will enable us to rule out background events involving particles that are not produced by neutrinoless double beta decay. This light will be detected along with the heat. The experiment’s cryogenic setup will also be improved.