Neutrinos are elementary particles postulated by Pauli in the 30’s as a “desperate attempt” to save the principle of energy conservation in radioactive beta decays. They have been observed 20 years later emerging from nuclear reactors and, since then, many of their physical properties have been established. There are three types, or "flavors", of neutrinos: electron neutrinos, muon neutrinos and tau neutrinos. If the rest mass of the neutrinos is different from zero, transitions among different flavors can take place when they propagate through space (“neutrino oscillations”). OPERA is aimed at performing a straightforward test of this phenomenon, trying to identify uniquely the appearance of tau neutrinos from a pure muon-neutrino beam propagating from Geneve to Gran Sasso.
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