The Majorana and Advanced Detectors Group addresses one of the most challenging research problems, determining the properties of neutrinos. These “ghost particles” pass through matter little or no interaction, making their detection nearly impossible. The Group leads an effort that built an underground, cryogenic, ultra-low background detection system in a former gold mine in South Dakota to try to determine if the neutrino is its own anti-particle. The answer to this question, a priority for the DOE Office of Nuclear Physics, is needed to understand the rarity of anti-matter in the Universe. The Group also participates in two neutrino experiments at ORNL, PROSPECT (at the High Flux Isotope Reactor) and COHERENT (at the Spallation Neutron Source). Additionally, Group members are developing and implementing gamma ray detector arrays with energy tracking that are needed at the next-generation of radioactive ion beam facilities to probe the structure of exotic unstable nuclei.
The Group led the Majorana Demonstrator Project in the Sanford Underground Research Facility in South Dakota, where 30 kg of ultra-pure Ge crystals enriched to 88% in 76Ge are precisely monitored for neutrinoless double beta decay. If this rare decay is observed, it will prove that the neutrino and the anti-neutrino are identical particles and that lepton number is not a conserved quantity. After 18 months of running, the Group recently released its first scientific result, setting a lower limit on the lifetime of this rare process to be 2e25 years. While this experiment continues to run, the Group is preparing to propose a 1-ton version called LEGEND with the goal of achieving a lifetime 100 times longer; this project that will require an international collaboration and over a decade to launch. Current research focusses on designing and characterizing prototype large inverted-coaxial point-contact detector for LEGEND and development of a detector based on a new scintillating plastic PEN.