For years, scientists have been puzzled by the imbalance between matter and antimatter — the mirror images of matter, bearing charges opposite to those of protons, electrons, and neutrons — in our universe. Theories suggest events of the Big Bang should have resulted in an equal amount of both, but somehow things turned in favor of matter, giving way to our material universe, consisting of galaxies, stars, planets, and the world we live in, and very less of antimatter.

The mystery still remains unsolved but an international team of physicists believes experiments at Italy’s Cryogenic Underground Observatory for Rare Events (CUORE) could help them find some answers. Specifically, the experiments conducted at the underground observatory could prove a major theory justifying the imbalance as true.

The idea revolves around neutrinos or the nearly massless particle that doesn’t interact with other matter, but acts as its own antiparticle, holding the ability to produce matter as well as antimatter version of itself. It is believed these ghostly particles, which are thought to spread throughout the universe, may have decayed asymmetrically soon after the Big Bang, producing most of the matter we see today and very less of its mirror image.

In order to prove this, scientists are working to detect “neutrinoless double-beta decay” — a situation in which natural decay of Tellurium dioxide crystals results in neutrinos giving away photons, electrons, and antineutrons. In this case, if the particle really acts as its own antimatter, the antineutrinos will cancel each other out and make up a “neutrinoless” decay, with only 2.5 megaelectronvolts of energy spike, which is less than a thousandth of a billionth of a joule.

A process as minute as this is extremely rare and requires a lot of effort to be detected. This is why the group took 988 Tellurium dioxide crystals to monitor at the CUORE observatory.

The site is buried within a mountain in central Italy keep away the external interference from the universe and contains an ultra-cold refrigerator (-459.6 degrees Fahrenheit). Here, the crystals, equipped with electronics and temperature sensors, sit peacefully, waiting to show the rare energy spike from the process in the form of a small increase in temperature.

The project started two months ago but they haven't detected any spike in energy, something that indicates “neutrinoless double-beta decay” is a lot rarer than previously thought. According to a release from the institute, a single atom of tellurium should go through the process once every 10 septillion years. 

That said, 988 crystals amount to some 100 septillion atoms, which means the researchers should see small energy spike in at least five atoms within next five years.

“Whenever you see a heat deposit on a crystal, you end up seeing a pulse that you can digitize. Then, you go through and look at these pulses, and the height and width of the pulse corresponds to how much energy was there,” CUORE member Lindley Winslow said in a statement. “Then you zoom in and count how many events were at 2.5 Mev, and we basically saw nothing. Which is probably good because we weren’t expecting to see anything in the first two months of data.”

The observation under this experiment will continue over next five years, but if this fails, the researchers will have the next-generation of the observatory, dubbed CUPID ready by then. It will monitor an even higher number of atoms to prove neutrinos indeed act as their own antiparticle. 

“If we don’t see it within 10 to 15 years, then, unless nature chose something really weird, the neutrino is most likely not its own antiparticle,” Winslow added. “Particle physics tells you there’s not much more wiggle room for the neutrino to still be its own antiparticle, and for you not to have seen it. There’s not that many places to hide.”