Researchers on the OPERA experiment (Oscillation Project with Emulsion-tRacking Apparatus) at the Istituto Nazionale di Fisica Nucleare’s (INFN) Gran Sasso Laboratory in Italy have announced the direct observation of a tau particle in a pure muon neutrino beam.
The beam is sent through the Earth from CERN, which is 730 km away, and has been sending billions of muon neutrinos from CERN to Gran Sasso since 2006.
The appearance of a tau particle is evidence that a muon neutrino has oscillated into a tau neutrino and must, therefore, have mass in order to be able to oscillate. Previous studies have recorded the disappearance of muon neutrinos, but this is the first evidence for the appearance of tau neutrinos.
These oscillations could help explain why current solar models predict more neutrinos should arrive at Earth than are seen, and contradict the Standard Model of particle physics in which neutrinos have no mass.
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