Scientists have long struggled to determine the negligible mass of neutrinos, the subatomic particles that could be matter and antimatter simultaneously. Now, a new study from researchers at the University of Tokyo (UT) might have discovered the key to revealing the mysterious mass of neutrinos: a calcium isotope.

Although neutrinos were discovered more than 60 years ago, scientists have yet to uncover some of their fundamental properties, such as their mass. The current experiment examined the calcium-48 isotope as it undergoes the process of neutrinoless beta decay in order to find a clue to the mass of these unique elementary particles.

Double beta decay occurs when an atom's parent nucleus decays into a daughter nucleus, which causes it to gain two protons, lose two neutrons and emit two electrons. This process was examined in the decay of calcium-48 to titatnium-38.

"The half-life of this decay depends on two factors: the unknown mass of neutrinos (which are part of the process, even though none are emitted) and the characteristics of the parent and daughter nuclei," said Javier Menéndez, co-author of the study and a researcher from UT. "This implies that, knowing these nuclear characteristics, and once this decay has been measured experimentally in one of the underground laboratories working on it, it will be possible to determine the mass of neutrinos."

The team's analysis of the decay of calcium-48 into titanium-38 is in unprecedented detail due to the use of complex quantum mechanics calculations.

"Our findings will make it possible to directly obtain neutrino mass when the half-life of this decay is measured experimentally," Menéndez said.

Although the findings hold promise, this unique decay is extremely rare and slow and has its roots in two simultaneous and weak decay processes, taking trillions of years to occur and proving very difficult to detect.

The team is now working on similar calculations for other neutrinoless double beta decays, such as those seen in germanium-76, selenium-82 and xenon-136.

"The most interesting thing would be to confirm that neutrinos are not emitted during double-beta decay, as that would imply by physical principles that neutrinos and antineutrinos are the same particle; that would be a massive discovery, a Nobel prize for sure," stresses Menéndez. "If that happened, we could say that neutrinos are Majorana particles, because they would be particle and antiparticle at the same time. This property was proposed by the Italian physicist Ettore Majorana in the '30s."

The findings were published in the March 15 issue of Physical Review Letters.