Cal Poly Physics Faculty and Students Participate in New Study That Reveals Progress in Unraveling the Mystery of Neutrino Particles – Cal Poly News

The answers “would explain to us how the universe works at the deepest levels and explain to us how to extend the laws of physics”

SAN LUIS OBISPO — Physicists searching for answers about the really big things we see in the universe and, more importantly, the infinitely small have made progress in unlocking the mysterious behavior of neutrinos. And Cal Poly faculty and students are playing a role.

A study recently published in the journal Nature describes how they put in place strict limits on the strange possibility that the neutrino is its own antiparticle.

“This is an incredible learning-by-doing experience for students over the years,” said Tom Gutierrez, a Cal Poly physics professor and one of the study’s co-authors, ” and it was an honor to be part of such a cutting edge project like this with so many amazing colleagues from all over the world.

For the past 10 years, his students have traveled to the Underground Cryogenic Observatory for Rare Events at Italy’s Gran Sasso National Laboratories, or CUORE (meaning “heart” in Italian). Built nearly a kilometer under solid rock, this world-renowned physics facility opened in 1989 and hosts neutrino and dark matter experiments. The laboratory is located near L’Aquila, in central Italy.

Gutierrez and the CUORE collaboration are looking for neutrinoless double-beta decay, a rare event that would help explain why the universe is full of matter instead of antimatter.

Neutrinoless double beta decay is a radioactive process in which an atomic nucleus releases two electrons but no neutrinos. The so-called “standard” double beta decay, which has already been measured, results in the release of two neutrinos. By observing this predicted but so far invisible event, physicists hope to estimate the mass of the neutrino and establish whether neutrinos and their antimatter counterparts, antineutrinos, are different particles.

“We didn’t find this nuclear decay rare – but putting strict limits on the process is an important part of the scientific process,” said Gutierrez, who, with support from the National Science Foundation, worked on this project and on related projects at Cal Poly since 2007. “If we were to find this decay, it would tell us how the universe works at the deepest levels and explain how to extend the laws of physics.”

Cal Poly is the only master’s-level institution involved in the project, working with a host of other world-class institutions, including Massachusetts Institute of Technology, Yale University, UC Berkeley, UCLA and Lawrence Berkeley National Laboratory (which conducts scientific research on behalf of the Department of Energy).

Neutrinos could provide the key to unraveling the mystery.

“Neutrinos are profoundly unusual particles, so ethereal and ubiquitous that they regularly pass through our bodies without our noticing,” according to Berkeley Lab. “Neutrinos are everywhere. They are invisible to the two most powerful forces in the universe, electromagnetism and the strong nuclear force, allowing them to pass through you, Earth, and almost everything else without interacting.

Despite an infinitely large number, their enigmatic nature makes them very difficult to study. All particles have antiparticles, their own antimatter: electrons have antielectrons (positrons), quarks have antiquarks, and neutrons and protons (which make up the nucleus of atoms) have antineutrons and antiprotons. But unlike all of those particles, it’s theoretically possible that neutrinos are their own antiparticles, according to Berkeley Lab.

“The ordinary matter of the universe – us, life, planets, stars, galaxies, etc. – is made up mostly of something physicists call ‘matter’ (as opposed to ‘antimatter’), but no one exactly why this form of matter survived,” Gutierrez said. “Nature shouldn’t favor matter over antimatter, and if equal amounts were created in the Big Bang, we literally shouldn’t exist right now because all matter and antimatter created in equilibrium should have been wiped out long ago.

“Yet here we are! All the familiar matter around us is apparently the tiny remnant of matter that hasn’t annihilated with its antimatter counterpart. For this reason, we represent the slight mysterious favoritism of nature towards matter. The rare nuclear decay we are looking for helps to understand this puzzle. However, the decomposition — if it happens — literally breaks the known laws of physics. Which is exciting! It is science!”

The experiment consists of an array of about 1,000 teller dioxide crystals cooled almost to absolute zero and equipped with extremely sensitive devices that measure temperature. If a specific increase in temperature occurs, this would indicate that a neutrinoless double beta decay has taken place. If the temperature does not rise, scientists can say with certainty that decomposition will not occur within a given period of time.

The detector itself is a technological marvel: “literally the coldest contiguous cubic meter in the known universe,” Gutierrez said of the device, which is shielded from environmental radiation by 4 tons of lead recovered from a Roman wreck, found in the remains of a ship. which sank off the Sardinian coast between 80 BC and 50 BC

“Cal Poly students have helped collect this data over the years and have made experimental shifts remotely during the pandemic to help collect more data,” Gutierrez said. “Normally I would send students to Italy to work on the experiment, but the pandemic has not allowed this activity since the beginning of 2020. In the future, there will hopefully be other opportunities for students to travel abroad to work on the project.”

See the Nature study by visiting: https://www.nature.com/articles/s41586-022-04497-4.

Photo information:
CUORE.jpg — The CUORE crystal array in Italy’s Gran Sasso National Laboratories Cryogenic Underground Observatory for Rare Events, or CUORE. The lattice is the set of 1,000 tellurium dioxide crystals that can cool almost to absolute zero. Built nearly a kilometer under solid rock, this world-renowned physics facility, which opened in 1989, hosts neutrino and dark matter experiments.
Photo credit: Yuri Suvorov

April 13, 2022
Contact: Tom Gutierrez
805-756-2455; tdgutier@calpoly.edu

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