Search for Neutrinoless Double Beta Decay with EXO-200

University Of Maryland, College Park, College Park MD

Investigators

Abstract

Neutrinos are the most mysterious and elusive of the fundamental particles known to physics. Although their existence was conclusively established in the 1950's, only within the last decade has it been demonstrated that neutrinos have a non-zero mass. The discovery of neutrino mass raises some intriguing questions. For example, we know that the heaviest neutrino is at least a factor of 100,000 times lighter than the next heaviest particle, the electron. What can explain this wide disparity in mass scales? Is the origin of neutrino mass fundamentally different from the other particles? And is this related to the fact that neutrinos are the only constituents of matter that carry no electric charge? Neutrino physicists have concluded that these questions can best be addressed by studying a rare nuclear process known as neutrinoless double beta decay. Double beta decay is the conversion of two neutrons in an atomic nucleus into two protons, while emitting two electrons to conserve charge. This reaction, if it occurs in nature, would be mediated by the exchange of a neutrino. Consequently the half life of the decay is a measure of the absolute mass of the neutrino, a quantity which is still unknown. In addition, many grand unification theories, which attempt to unite three of the fundamental forces into one, either predict that double beta decay should occur, or predict that it should be forbidden. Therefore an experiment which can observe or rule out this process will play a key role in our understanding of matter at its most basic level. In this proposal, the PI requests funds to start a new group at the University of Maryland to collaborate on EXO-200, an experiment to search for the neutrinoless double beta decay of Xenon-136, and to significantly expand and broaden the tools used by the experiment to monitor, identify, and eliminate sources of electronegative impurities in the xenon. The experiment will begin taking data in 2007. In addition to the basic science goals described above, the research proposed here will have a significantly broader impact. The radiation detector technology being developed for EXO-200 has potential applications in other fields such as nuclear medicine and homeland security. The PI also proposes to initiate an outreach program in the public schools in Carlsbad New Mexico and the Shenandoah Valley of Virginia, both of which are underserved areas.