Neutrino-less double beta decay probes mystery of matter dominated universe

Almost all substance of the universe is made of "matter", not "anti-matter". This is a mystery of "the matter dominated universe". The leptogenesis scenario is expected as an attractive solution for the mystery of this "matterdominated universe". One of the key point of the leptogenesis scenario is the lepton number non-conservation that means "anti-particle" and "particle" can convert to each other. "Observation of neutrino-less double beta decay" provides direct evidence of lepton number non-conserving process. The first theoretical indication of "neutrino-less double beta decay" is in 1939. It is pointed out by scientist in nuclear physics. And the rate of "neutrino-less double beta decay" is predicted to be rare. Over 80 years since the indication already passed without observation of neutrino-less double beta decay. At the present day, many scientists of nuclear physics, particle physics and astroparticle physics are interested in the neutrino-less double beta decay in the world. Because one of that, in recent years, the sensitivity of the detector system for neutrino-less double beta decay measurement is dramatically improved. The observation of neutrino-less double beta decay might be coming in a few years, or ten years at the latest. (author)