The current generation of neutrino detectors such as the Super-Kamiokande can detect and distinguish between electron and muon neutrinos. Most experiments involving neutrinos involve electron neutrinos which are much more common in our low-energy world, but some current neutrino detectors are sensitive to the other two as well. The massive leptons are the electron, muon and tau, and each of them has an associated neutrino. Further detailed analysis of this data from Super-Kamiokande is consistent with neutrino oscillation, so this is the first clear experimental evidence supporting a non-zero mass for the neutrino. Neutrino oscillation has been hotly debated over the past few years because its existence implies a mass for the neutrinos.
Their interpretation of this result is that the deficiency is caused by "neutrino oscillation" in which a number of muon neutrinos are transmuted into tau neutrinos which are undetectable. From the nature of the interactions of cosmic rays in the upper atmosphere, two muon neutrinos are expected for every electron neutrino, but they found a ratio of only 1.3 to 1. Kearns, Kajita and Totsuka report the detection of 5000 neutrino events in two years of measurement. The 11,000 hand-blown photomultiplier tubes are half a meter in diameter and coated inside with a thin layer of alkali metal to detect the Cerenkov radiation from the interactions of either electron neutrinos or muon neutrinos. The 50,000 tons of water in the tank detector is so pure and transparent that light passes 70 meters before its intensity drops to half, compared to a few meters in a typical swimming pool. 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. Neutrinos Super-Kamiokande Neutrino Detector
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