CHORUS experiment

People involved

CHORUS: CERN Hybrid Oscillation Research apparatus

In the CHORUS experiment, we have analysed the interactions of a pure neutrino beam of a particular type (the muon neutrino νµ) generated by the large CERN SPS accelerator between 1994 and 1997. Our detector has an extremely high spatial resolution and is very sensitive to the detection of interactions generated by another type of neutrino (the tau-neutrino ντ). This would have been the sign of an oscillation between the two types of neutrinos. The search is now complete and no tau neutrino event has been found. This places a new limit on the νµ-ντ oscillation probability in the domain of neutrino masses relevant for astrophysics and cosmology. The observation of such a neutrino oscillation phenomenon would demonstrate that neutrinos have mass like all the other constituents of matter and can thus contribute to the dark matter of the Universe – i.e. matter whose existence is inferred only through its gravitational effects. There is evidence that this matter is mainly composed of particles that have survived from the Big-Bang and are not the usual protons, neutrons and electrons that constitute the ordinary matter. Big-Bang cosmology indeed predicts that there are about 1 billion times more neutrinos than protons in the Universe.

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