Neutrinoless double beta decay and direct searches for neutrino mass
  Study of the neutrinoless double beta decay and searches for the manifestation of the neutrino mass in ordinary beta decay are the main sources of information about the absolute neutrino mass scale, and the only practical source of information about the charge conjugation properties of the neutrinos. Thus, these studies have a unique role in the plans for better understanding of the whole fast expanding field of neutrino physics. 
Craig Aalseth, Henning Back, Loretta Dauwe, David Dean, Guido Drexlin,   Yuri Efremenko, Hiro Ejiri, Steven Elliott, Jon Eng...