The helicity of neutrinos has only been observed in two states: left-handed neutrinos and right-handed antineutrinos, with the possibility of additional states depending on whether neutrinos are their own antiparticles. The MAJORANA DEMONSTRATOR experiment, located almost a mile underground, aims to determine if neutrinos are their own antiparticles through the observation of neutrinoless double-beta decay. This event has never been conclusively detected and, if proven, would require a rewrite of the Standard Model of Particles and Interactions. MAJORANA is in competition with another germanium experiment, GERDA, to determine which has the lower background noise for the final one-ton detector.
https://newscenter.lbl.gov/2012/05/16/majorana-demonstrator/