Super-Kamiokande Neutrino Detector
Inside Mount Ikenoyama in Japan within an active zinc mine is a remarkable tank of ultrapure water which is the world's most sensitive neutrino detector as of 1999.
Kearns, et al.
Muon and Tau Neutrinos
The massive leptons are the electron, muon and tau, and each of them has an associated neutrino. The current generation of neutrino detectors such as the Super-Kamiokande can detect and distinguish between electron and muon neutrinos. When a muon neutrino interacts with a nucleus, it can produce an energetic muon which travels only a short distance, emitting a sharply outlined cone of Cerenkov radiation which can be detected by photomultiplier tubes. An electron neutrino interaction can produce an energetic electron, but the Cerenkov cone from this interaction differs significantly from that of the muon. The electron generates a shower of electrons and positrons, each with its own Cerenkov cone. This smears out the circle of light which hits the detectors; the diffuse circle at the photomultipliers is the signature of the electron neutrino. Tau neutrinos are not detected by these detectors because the neutrino energies are not sufficient to produce tau particles (which are about 3500 times the mass of an electron).
The first clear experimental evidence for the difference between electron and muon neutrinos came from an experiment conducted at Brookhaven in 1962. The two reactions indicated would have been equally probable if electron and muon neutrinos were the same.
Since the electron and muon neutrinos are distinct, the second reaction above violates conservation of lepton number.
Kearns, et al.