THE OUTPUT. “When a neutrino interacts with a neutron in the water, it can produce a muon or an electron, depending on its flavour. The T2K experiment detects the muons and electrons and discriminates between them, thereby identifying the flavour of the impinging neutrino and measuring the oscillation probability of muon-to-electron neutrino conversion.”
https://www.nature.com/articles/d41586-020-01000-9