Physicists in Britain and the US are obtaining tantalising evidence that a fourth, massive neutrino exists. It appears from time to time during the beta decay of a nucleus, when a neutron changes into a proton, spitting out an electron and a neutrino. The usual electron-neutrino emitted in the process has little or no mass at all.
The new experiments seem to confirm a curious effect observed in the laboratory by a Canadian physicist in 1985, and which few took seriously at the time. If a massive neutrino does exist, it could have far-reaching implications for theories of particle physics and cosmology.
Scientists at the University of Oxford and at the Lawrence Berkeley Laboratory in California have recently been measuring the energy spectrum of electrons emitted during the beta decay of certain nuclei. The maximum, or 'end point', energy of the electrons can be used to estimate the mass of ...
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