Particle physics: Closing in on matter–antimatter asymmetry

Hints of a difference between the fundamental behaviour of neutrinos and of antineutrinos, their anti-matter counterparts, are reported in Nature this week. These observations from the T2K experiment at the Super Kamiokande detector in Japan may have implications for our understanding of the formation of the Universe, if confirmed.

It is thought that finding asymmetry in the physical properties of neutrinos and antineutrinos may help us understand the origin of the current prevalence of matter over antimatter in the Universe. This asymmetry is known as charge-conjugation and parity reversal (CP) violation.

Researchers working on the T2K experiment used the Super Kamiokande detector to observe neutrinos and antineutrinos generated 295 kilometres away at the Japanese Proton Accelerator Research Complex (J-Parc). As they travel through the Earth, these particles oscillate between different physical properties known as flavours. The T2K collaboration found a mismatch in the way neutrinos and antineutrinos oscillate by recording the numbers that reached Super Kamiokande with a flavour different from the one they had been created with.

After analysing nine years’ worth of data, the T2K experiment reached a level of statistical significance high enough to provide an indication that CP violation occurs in these fundamental particles. More precise measurements are needed to confirm these findings. However, these measurements do strengthen previous observations and pave the way towards a future discovery. A new generation of experiments under construction might provide an answer to the problem of the ‘missing’ antimatter in the next ten years.