T2K’s first search for violation of charge-parity symmetry (CP violation) was published in Physical Review Letters as an Editors Suggestion in the April 14 edition. This is the first result from T2K that simultaneously analyses both neutrino and antineutrino data sets.
The international T2K (Tokai-to-Kamioka) collaboration searches for CP violation with both neutrino and antineutrino beams, and is the world’s first experiment to publish an exclusion of CP conservation at 90% CL. The experiment, hosted by KEK (High Energy Accelerator Research Organization) and ICRR (Institute for Cosmic Ray Research), consists of high intensity beams of muon neutrinos (or muon antineutrinos) that are produced at J-PARC (Japan Proton Accelerator Research Complex) on Japan’s east coast, and fired towards the Super-Kamiokande detector 295 km away in Gifu Prefecture. On the way, the neutrinos and antineutrinos spontaneously change ‘flavor’, with muon neutrinos changing to electron neutrinos and muon antineutrinos changing to electron antineutrinos. A difference in the rates of oscillations in separate neutrino and antineutrino beams would be the signature of an imbalance between particles and antiparticles, which would be expected to reveal new phenomena beyond the Standard Model of particle physics.
The first CP violation study by T2K was published in April, and detected 32 electron neutrinos and 4 electron antineutrinos, to be compared to expectations of 24 neutrinos and 7 antineutrinos if there were no CP violation. Recently, thanks to outstanding beam delivery by the J-PARC facility, the T2K experiment has finished collecting data in neutrino mode that has doubled the amount of neutrino data available, and its results are expected to be presented later this year.
“The 2016 CP violation search was a successful first look at both neutrinos and antineutrinos. We look forward to presenting results from our new data set in the summer of 2017,” said T2K Spokesperson Prof Tsuyoshi Nakaya (Kyoto University).