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Not mentioned is that Ray Davis also discovered the solar neutrino deficit, a problem that was solved in the last few years by scientists here at Penn. The reason why Prof. Davis's neutrino experiment in the Homestake gold mine only detected 1/3 as many neutrinos as predicted by the standard solar model is that the electron-type neutrinos produced by the sun transform into muon-type and tau-type neutrinos in-flight on their way from the sun. This in turn demonstrates that neutrinos have mass. Since Prof. Davis's experiment was only sensitive to electron-type neutrinos, he saw an apparent deficit.
With little more than a tank of dry cleaning fluid--carbon tetrachloride--he discovered a fundamental fact about the most elementary particles in the universe.