T2K, the Tokai-to-Kamioka, uses a beam of muon neutrinos to study the phenomenon of neutrino oscillations.
The beam is produced at the J-PARC accelerator facility in Tokai-mura, on the east coast of Japan, and the neutrinos are detected 295 km away at the Super-Kamiokande detector. Over the 295 km baseline, some of the muon neutrinos oscillate to tau or electron neutrinos. T2K observes the appearance of these electron neutrinos as well as the deficit of muon neutrinos due to the oscillations.
The muon neutrino to electron neutrino oscillation channel is of particular interest since the probability of oscillations can be different for neutrinos and antineutrinos, an effect called CP violation. In 2013, T2K showed the first observation of these oscillations, opening the door for future CP violations searches. Now T2K is collecting data with both neutrino and antineutrino enhanced beams with the goal of observing the first indications of CP violation in neutrino oscillations.