Our universe is filled with neutrinos. The sun in particular is an abundant source. Yet neutrinos interact only weakly with ordinary matter, so that delicate experiments are necessary to detect them. Although a lot of progress was made in recent years, much remains to be done to constrain their properties, which are a crucial ingredient in particle theories. We are engaged in two experiments aiming at a better determination of the sizes and nature of the masses, and of the mixings between mass and weak eigenstates.

First we are participating to EXO, which is searching for the neutrinoless double beta decay of 136Xe. This decay is possible if neutrinos have small, but non vanishing, masses of the Majorana type, making neutrinos identical to antineutrinos. Superior sensitivity will be achieved thanks to novel techniques, allowing to largely suppress the background. A first set-up, EXO-200, with 200 kg of xenon highly enriched in 136Xe, is being installed in Stanford, the home-base of the experiment. After debugging the detector will be moved to the WIPP underground lab in New Mexico and data taking is expected to begin in fall 2007. We built the cryostat of EXO-200, and helped in selecting radiopure components with our germanium detector in the “La Vue des Alpes” tunnel. The experience gained with EXO-200 will be used to design the final detector, which will have a mass of order 1 t. We are now participating to R&D on a scheme to detect the barium ion left behind in double beta decay. This feature, if it can be made to work, will give EXO an unprecedented sensitivity to the neutrino mass, extending down to a few hundredths of an eV.

Second we are contributing to the OPERA experiment, aimed at demonstrating that muon neutrinos oscillate into tau neutrinos, as suggested by experiments with atmospheric neutrinos. Muon neutrinos from the CERN CNGS beam are directed toward the Gran Sasso underground laboratory, at a distance of 530 km, where the detector is installed. Thanks to the use of emulsions with superior spatial resolution, it will be possible to identify interactions with a tau in the final state on an event by event basis. This feature makes OPERA unique. The detector is in the final stage of completion. Data taking should start in the fall of 2007, and will continue for five years. After having contributed to the construction of the detector, we are now concentrating on the scanning of emulsions and data analysis.