Nuclear Physics Division

Scientific goals :

Neutrinos are elementary particles produced abundantly in stars, in the Earth's atmosphere and in the cores of nuclear power plants. In 2006 CEA/IRFU and CNRS/IN2P3 have decided to officially launch the construction of the Double Chooz experiment. Two identical detectors are to be installed near the Chooz nuclear power plant, in the French Ardennes, at different distances from the reactors. This experiment will allow a precise measurement of the last unknown property of neutrinos: their oscillations.

Neutrinos are elementary particles that interact very weakly with matter: at most one in ten billion is stopped while going through our planet. They exist as three different types, and are able to change from one type to another through a peculiar quantum property, "oscillation". Three parameters enter the equations that govern the frequency of these oscillations. (The parameters are called "mixing angles", as they characterize the mixing proportions between the various neutrino types.) Two of them have already been measured. The earlier Chooz experiment, which was conducted at the same site between 1997 and 1999, was able to show that oscillations corresponding to the last, third parameter are infrequent: its value must thus be small. It is crucial however to measure it as, besides putting a finishing touch to the Standard Model of particle physics, its value is needed in the preparation of experiments that aim to understand the origin of the matter-antimatter asymmetry in the Universe. Five physics Nobel prizes have already rewarded discoveries about neutrinos.