LEGEND-200 will explore the nature of neutrinos

Sheltered under a mile of rock in Italy’s Abruzzo region, scientists are scrambling to unravel the secrets of the universe’s lightest particles of matter.

When a radioactive process called double beta decay occurs, four particles are usually emitted: two negatively charged electrons and two (anti)neutrinos, tiny neutrally charged particles. Located at the Gran Sasso National Laboratory, the LEGEND-200 (Large Germanium Enriched Experiment to Search for Neutrinoless Double Beta Decay) experiment is designed to find out if this process can occur without neutrinos being observed at final. The answer could change our understanding of how matter arose.

Such “neutrinoless double beta decay” is very rare, if it occurs at all. And determining that a decay produces electrons but not neutrinos can be difficult, especially since neutrinos are everywhere (thousands of them pass through our bodies every second) and are usually generated when background radiation interacts with instrument components. .

So scientists are trying to “pick very low-radioactive materials and come up with lots of clever ways to weed out background particles,” says Michelle Dolinski, a particle physicist at Drexel University who is not involved in the project.

LEGEND-200 is equipped with slightly radioactive germanium crystals, which act both as a source of beta decays and as a neutrino detector. To shield it from surrounding particles, the entire instrument is immersed in a cryogenic tank protected by water and liquid argon. This core is surrounded by green optical fibers and a reflective layer that repels any foreign particles.

If LEGEND-200 were to observe neutrinoless double beta decay, that would mean that, unlike protons, electrons, and other elementary particles (each of which has an “antiparticle” with which they annihilate if they come into contact), neutrinos are their own antiparticles and can destroy each other. In such a case, the double double beta decay would produce two neutrinos that would immediately annihilate, so that none would be left. “This is an important ingredient in trying to understand why there was more matter than antimatter in the early universe and why the cosmos is the way we see it today,” Dolinski says.

Laura Baudis, a LEGEND collaborator and an experimental physicist at the University of Zurich, is excited to see what this experiment uncovers when she starts collecting data this year. “There are a lot of things we don’t know about neutrinos,” she stresses. “They really are still full of surprises.”

Joanna Thompson

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