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Introduction

There is no direct evidence for neutrino mass from any laboratory experiment. Nevertheless, there are strong hints from theory, astrophysics, and cosmology that the neutrinos may have small masses. It has long been known that the observed high energy solar neutrinos produced in decays are suppressed by a factor of two to three compared to expectations of the standard solar model. This by itself could be accounted for by astrophysical or nuclear physics effects. However, there are now four experiments of three types, which are sensitive to different parts of the spectrum. By comparing the experiments it is possible to infer that most of the suppression is in the middle of the spectrum, associated with the line and the lower energy part of the \ spectrum. This is inconsistent with any known astrophysical or nuclear physics explanation, and strongly suggests new neutrino properties, such as MSW matter-enhanced neutrino oscillations. This conclusion can be reached by using any two of the three types of existing experiments. Future experiments will yield considerable new information. By searching for spectral distortions, day/night effects, and anomalous ratios of neutral current to charged current events it should be possible to either confirm or falsify the need for neutrino oscillations, independent of astrophysical uncertainties.




Mon Nov 27 19:39:39 EST 1995