To answer the question of the matter-antimatter asymmetry in the universe, we have to understand how the matter-antimatter transformation can occur. The study of the baryon- or lepton-number nonconservation will provide a big hint to that.。

The neutrinoless double-beta decay is considered to provide a unique opportuinity to search for the kepton-number nonconservation, since it requires the equivalence between neutrino ans antineutrino in addition to the exsistence of finite masses of the neutrinos and/or the right-handed current in the weak interaction.

Since the neutrinoless double-beta decay is an extremely rare process characterized with the half lives as long as 10^26 years or more, huge quantity of the source material together with high-sensitivity and extremely low-background detector are crucial. The CANDLES experiment is expected to be the solution for that. It uses a high purity crystalsof CaF_2 as the detector material, and detects the signals of the double beta decay of 48Ca containdin the crystal itself. Now the development for the upgraded detector based on the bolometer technique is in progress. For detail, pleas visit the web site of CANDLES.