Sterile Neutrino Results

The group of scientists monitoring neutrino oscillations at the giant underground Super-Kamiokande detector in Japan believe that muon neutrinos are probably transforming into tau neutrinos exclusively and not into "sterile" neutrinos. Some theorists have proposed that in addition to the standard three neutrino types (electron, mu, and tau) an extra neutrino should exist, one which interacts even more weakly than the others. In early Kamiokande results a shortfall of observed muon neutrinos (created when high energy particles strike the Earth's atmosphere) was explained by saying that on their way to the underground detector they had turned into either tau or sterile neutrinos. New analysis of data in Japan now rule out the sterile-neutrino part of the scenario. (Fukuda et al., Physical Review Letters, 6 November; Select Article.)