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neutrino graphic
The Super-Kamiokande Experiment research team, a group of 120 scientist from around the world, announced their discovery of evidence for non-vanishing neutrino mass. Until this evidence, physicists assumed zero mass for the neutrino. Careful measurements of the end point of the beta spectrum in nuclear beta decay set upper limits for the mas of the emitted neutrino that were very small indeed. In 1929 Wolfgang Pauli wrote to Hans Wilhelm Geiger and Lise Meitner that there may be a massless neutrino emitted in nuclear beta decay. Enrico Fermi gave a theory for this in 1934.Through the careful work of many physicists around the world these ideas were confirmed, and for many decades it was believed that the neutrino was indeed a massless particle.

To read about original and important contributions that were historical milestones in the study of nuclear beta decay, see Lise Meitner and Chien Shiung Wu.

In the last few years physicists have been reporting, in various types of observations, that there seems to be evidence that the neutrino is not massless. Observations however indicate the mass is exceedingly small - much smaller than that of any known massive particle. How much smaller is indicated in the graphic at left.

Physicists at University of California, Irvine have prepared a website from which you can learn more about neutrinos and `what all the excitement is about'.

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