This award is for a collaborative research and development undertaking between the University of Stanford and the University of Alabama towards the feasibility of a high pressure gas phase detector using enriched Xenon for the detection of neutrino-less double beta decay. Research and Development is to proceed within the broader EXO collaboration to advance detection with liquid Xenon by the introduction of tagging and to a high pressure gas phase using Xe with low background. The proponents envision applying tagging with Barium for the liquid detector to drastically reduce the radioactive background and allow an unambiguous measurement of unprecedented sensitivity. This work will be mainly carried out by the University of Stanford group. The developments of the gaseous detector are not as advanced as the liquid case and the group from the University of Alabama will be exploring the characteristics of such a detector. It is expected that at completion of this project, there will be results to guide the detector development and technology selection for the ton-class of neutrino less double beta decay experiments for the Deep Underground Science & Engineering Laboratory.
This project developed some of the tools required to answer questions like: what is the mass of the neutrino, the lightest particle in nature? Is the mass of the neutrino produced by the same mechanism that gives mass to all other particles? Is the fact that neutrinos are the only neutral elementary constituent of matter related in some way to the fact that neutrinos are so much lighter than other constituents? It is expected that such questions will be answered by searching for a very rare process, called neutrinoless double beta decay. This is a process in which a particular nucleus, in out case the isotope 136 of xenon, decays into another nucleus with two more protons and two fewer neutrinos. Neutrinoless double beta decay has never been observed and is expected to be exceeding rare, making its detection rather challenging. Indeed natural radioactivity from most standard materials (and the human body) can easily overwhelm the measurement. Under this grant some R&D was performed to reduce such radioactive backgrounds and devise new methods to better discriminated between double-beta decay events and other sources of radioactivity. In particular out work advanced the possibility of collecting and identifying the atom (barium) produced by the double-beta decay of xenon. Other applications of this work could arise from the field of detector of nano-trace contaminations, where single atoms of a substance could be detected in the bulk of another. In the problem of advancing this research, a prototype detector, called EXO-200, recently made the first detection of the 2-neutrino double beta decay in 136Xe, a process related to the more interesting neutrinoless decay. The process detected by EXO-200 is the slowest ever observed in our universe, some 100 billion time slower than the age of the universe.
