The T2K Collaboration has published in Nature new results showing the strongest constraint yet on the parameter that governs the breaking of the symmetry between matter and antimatter in neutrino oscillations. Using beams of muon neutrinos and muon antineutrinos, T2K has studied how these particles and antiparticles transition into electron neutrinos and electron antineutrinos, respectively.
The parameter governing the matter/antimatter symmetry breaking in neutrino oscillation, called δcp phase, can take a value from -180º to 180º. For the first time, T2K has disfavored almost half of the possible values at the 99.7% (3σ) confidence level and is starting to reveal a basic property of neutrinos that has not been measured until now. This is an important step on the way to knowing whether or not neutrinos and antineutrinos behave differently.