Physics Professor, Students Explore Mysteries of the Universe in Italian Underground Lab
The above image shows the CUORE crystal array in Italy’s Gran Sasso National Laboratories’ Cryogenic Underground Observatory for Rare Events, or CUORE. Photo by Yury Suvorov, courtesy of the CUORE Collaboration
In an underground lab in the Italian mountains that contains the coldest temperatures known in the universe, more than 150 leading international scientists try to solve one of the biggest mysteries in particle physics.
Among the researchers, who hail from top educational institutions in the United States, Europe and Asia, is Cal Poly physics professor Thomas Gutierrez. Gutierrez is the principal investigator of a recently-awarded, $340,000, three-year National Science Foundation Grant.
At Gran Sasso National Laboratory near Assergi, Italy, Gutierrez, his students and other scientists explore unproven theories related to nuclear decay, also known as radioactive decay, the process by which an unstable atomic nucleus loses energy through radiation. The Gran Sasso lab is the largest underground laboratory in the world devoted to neutrino and astroparticle physics.
Their work strives to better explain why the universe is full of matter, and to address other mysteries that have befuddled scientists for generations.
Cal Poly’s NSF grant covers costs associated with travel and experiments for the research that involves Bailey College of Science and Mathematics students.
“If you can find something that breaks the laws of physics, then that’s discovery,” said Gutierrez whose research interests include nuclear particle physics, quantum information and neutrinoless double beta decay. “We’re looking for a type of nuclear decay that is currently forbidden by the (existing) laws of physics. It’s not supposed to happen. So, if it does — which is what we’re looking for — it tells you a lot about the way the world works.”
The research continues scientific collaboration started under the international CUORE (Cryogenic Underground Observatory for Rare Events) program, a particle physics experiment at the Gran Sasso lab primarily designed to search for neutrinoless double beta decay, a very rare nuclear decay process, by using an array of extremely sensitive cryogenic bolometers that measures radiant heat by converting it into an electrical signal. The lab’s next generation experiment under development is called CUPID (CUORE Upgrade with Particle Identification).
Gutierrez’s field of study focuses on neutrinos, the tiny particles with very slight amounts of mass. Abundant in the universe at the big bang, the cosmic explosion that marked the beginning of the universe, and traveling at near lightspeeds, neutrinos can also come from violent bursts like exploding stars. Neutrinos are often created by radioactive decay. Because they don’t interact very much and are neutral, they can help explain enigmas of the universe related to matter and antimatter.
In modern physics, all particles have antiparticles, their own antimatter counterpart: electrons have antielectrons (positrons), quarks have antiquarks, and neutrons and protons (which make up the nuclei of atoms) have antineutrons and antiprotons.
“Under the laws of physics, there should have been equal amounts of matter and antimatter, and they should have all annihilated, gone away, and we shouldn’t exist,” Gutierrez said. “Yet this little sliver of matter that got left over is us. Why do we even exist? Why is that sliver there at all? So that’s kind of a puzzle.”
Under a longstanding scientific theory, neutrinos may be their own antiparticles. But this concept remains unproven. The work at Gran Sasso hopes to reveal the possibility of neutrinoless double-beta decay, a radioactive process in which an atomic nucleus releases two electrons but no neutrinos. Observing this decay would support the hypothesis that neutrinos are their own antiparticles — a significant finding in particle physics.
“If neutrinoless double beta decay happens, it tells us all this information about the foundations of how matter — not just this matter, but all matter — exists,” Gutierrez said. “This is very powerful.”
Gutierrez and the international science team are collaborating on a study of tellurium dioxide crystals, a mixture of the element tellurium and oxygen.
“There is a hypothesis that a tellurium isotope can undergo a neutrinoless double beta decay,” Gutierrez said.
About a third of the tellurium nuclei in a chunk of crystal under observation is the right isotope, Gutierrez said.
“The idea is to use a detector out of this crystal where it measures its own decay,” Gutierrez said. “It will deposit a very certain amount of energy, raising the temperature, which we can observe. Through this testing, in a best-case scenario, what we’d like to be able to say is whether or not the neutrino is its own antiparticle.”
The Italian lab facility is below nearly a mile of rock, which shields cosmic rays and other natural radioactivity in each direction and features a protective, six-centimeter-thick shield fabricated from boiled-down lead retrieved from an ancient Roman merchant shipwreck. The ancient lead used as a protective guard for the lab’s research is free of its own radioactive material because of a natural process that takes centuries to transpire, demonstrating the effectiveness of centuries-old lead for science.
The cold research conditions have been designed for temperatures of around 10 millikelvin or -441.74 degrees Fahrenheit — the coldest volume of its size anywhere in the universe. Such temperatures help with particle science, because as particles cool, they move far slower, allowing scientists to more precisely study their behaviors.
People have been “pounding their heads against the wall trying to understand” theories around antimatter versus matter, and how neutrinos might be involved, Gutierrez said.
“There’s a lot of different avenues people have been exploring, but about 30 years ago this idea arose that if this decay occurs, then that tells us about the properties of matter, and that it would imply that the universe actually does favor matter over antimatter ever so slightly,” Gutierrez said.
Cal Poly students already have contributed and will continue to do so, including Reagen Garcia. Part of Garcia's work, which can be conducted at Cal Poly, includes remote detector operation shifts, monitoring the experiment taking place in Italy from afar.
“CUORE needs to be constantly monitored, so remote detector operation shifts are an important part of the experiment,” Garcia said. “The grant will help students take part in these shifts. It will also help send students to Italy or other universities that are part of the collaboration.”
Garcia also conducted summer work at Yale’s Wright Laboratory, a collaborating institution for the CUPID experiment, where Garcia conducted testing of a particle detector system.
“It was exciting to be part of such detailed, specific aspects of experimental design,” Garcia said. “This summer at Yale was the most exciting and rewarding research experience I have had the opportunity to be part of.”
Garcia added that the project’s research experience has helped her learn many “important skills for graduate school, and it was a confirmation that this is the field I want to go into after I graduate.”
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