Scientists are getting closer to discovering whether neutrinos and antineutrinos are in fact the same particles — known as Majorana neutrinos.

The theory, proposed by Italian physicist Ettore Majorana in the 1930s, could explain why neutrinos have mass and why the Universe contains more matter than antimatter. Azusa Gando at Tohoku University in Sendai, Japan, and her colleagues in the KamLAND-Zen Collaboration carried out the most sensitive search so far for radioactive decay indicative of Majorana neutrinos, using an underground detection facility containing a huge balloon filled with purified xenon.

The team's results, although negative, constrain the upper limit of the mass of Majorana neutrinos to 61–165 millielectronvolts. However, the detector's sensitivity must be pushed even further to prove Majorana's theory, the researchers say.

Phys. Rev. Lett. 117, 082503 (2016)