Search for Majorana neutrinos

Whether there exist elementary particles having Majorana nature is one the fundamental open question that has persisted since the 1930s. The only practical experiments to test the Majorana nature of neutrinos is the search for neutrinoless double-beta decay, which has been a major challenge for nuclear and particle physicists. In the 2000's, a number of experiments using advanced technologies have been planned, and some of which have already achieved significant improvements in the search sensitivity. In this article, the current status of the neutrinoless double-beta decay searches are summarized, reviewing the progress of KamLAND-Zen, which recorded the world best sensitivity in the effective Majorana neutrino mass limit.