T2K Results Restrict Possible Values of Neutrino CP Phase

The results published in Nature are a major step forward in the study of the difference between matter and antimatter

The T2K Collaboration has published 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 have not been measured until now.

This is an important step on the way to knowing whether or not neutrinos and antineutrinos behave differently. These results, using data collected through 2018, have been published in the multidisciplinary scientific journal, Nature on April 15.

Fig.2 Event displays of candidate electron neutrino (left) and electron antineutrino (right) events observed in Super-K from the T2K neutrino beam. When an electron neutrino or antineutrino interacts with water, an electron or positron is produced. They emit a faint ring pattern light, which is detected by about 11,000 photo-sensors. The color in the displays represents the photon detection timing.

 Reference:

Constraint on the Matter-Antimatter Symmetry-Violating Phase in Neutrino Oscillations
DOI: 10.1038/s41586-020-2177-0
Nature Vol. 580, pp. 339-344

Link to Press Release: Spanish, English

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