This award provides base support for the group to continue to participate in the Enriched Xenon Observatory (EXO) program to search for neutrino-less double beta decay in 136-Xenon, a nuclear process which could hold clues into the nature of neutrinos. Observation of this decay would imply that neutrinos are Majorana particles, i.e. their own antiparticles, with profound implications on our understanding of the pattern of masses of fundamental particles and of the structure and evolution of the early universe.
The EXO-200 experiment, a 200-kg enriched liquid xenon detector is now running underground at the Waste Isolation Pilot Plant (WIPP) in New Mexico. This group will also take part in the development and design of a more sensitive tonne-scale EXO experiment (full-EXO) to follow EXO-200. With the planned research at UMass, the group will provide key input to the design of a full-EXO experiment with sensitivity to neutrino masses as small as 10 meV by: i) optimizing the optical response and VUV detection efficiency of the detector, and ii) supplying a single Barium ion source, a possibly game-changing tool for the realization of the EXO-specific background suppression scheme which looks for the appearance of Barium ions following 136-Xe double beta decay.
Broader Impacts: Noble liquid detectors are finding applications in medical imaging devices as well as in remote monitoring of nuclear power plant fuel composition. The ultra-low background methods developed for detectors like EXO-200 have taken radioactive contamination to levels considered impossible to achieve just twenty years ago. Processes of interest for the electronics industry now require similar levels of radio-purity in their manufacturing lines. Work with EXO-200 and EXO provides ample opportunities for graduate students to perform cutting edge research and experience working in a medium-sized international scientific collaboration.
