INSPIRE: Development of a Technique to Detect Single Ba Atoms in Solid Xe Matrix Toward Be Tagging in nEXO

Colorado State University, Fort Collins CO

Investigators

Abstract

This INSPIRE project is jointly funded by the Experimental Nuclear Physics and the Atomic, Molecular and Optical Physics programs in the Physics Division, the Chemical Measurement and Imaging program in the Chemistry Division (both Divisions are in the Mathematical and Physical Sciences Directorate of NSF), and the Office of Integrative Activities. The award supports the discovery and development of a technique to detect and uniquely identify one barium atom in five tons of liquid xenon using novel methods of laser spectroscopy. The ultimate goal is the discovery of a rare radioactive decay, called neutrinoless double-beta decay, of the isotope 136Xe. The proposed single-Ba detection technique would make the experimental search for this decay significantly more sensitive. A discovery of this decay would show that neutrinos are the same as anti-neutrinos. This would fundamentally change our view of the elementary components of matter and would potentially contribute to an understanding of why there is more matter than anti-matter in the universe. Instruments and methods developed in this project may be relevant to the kinds of matrix isolation experiments used in chemistry. The proposed work also has very important educational and outreach components, as it connects high school teachers to state-of-the-art research. A major breakthrough in detecting barium atoms in solid xenon at the single atom level has recently been achieved. Continued interdisciplinary research will be supported in which individual atoms of Ba will be imaged by laser-induced fluorescence while trapped in a matrix of solid Xe grown first on a sapphire window and then at the end on an optically accessible probe. Research on grabbing and detecting Ba atoms on a probe from liquid xenon is also planned. The ultimate goal of the work is to capture and detect a single 136Ba daughter of neutrinoless double-beta decay of 136Xe, advancing what may be the ultimate background suppression method for ton-scale experiments. The possibility afforded by this technique is unique to 136Xe and, coupled to a second phase of the nEXO detector, could substantially improve its sensitivity beyond 10^28 year half life, allowing the exploration of part of the normal hierarchy regime of neutrino mass. The observation of neutrinoless double-beta decay answers a grand challenge in nuclear physics, whether or not 2-component Majorana fermions exist in Nature. This may shed some light on the puzzling fact that neutrinos have a finite mass and yet they are so much lighter than all other known particles. In addition the observation of neutrinoless double-beta decay would provide a measurement of the neutrino mass scale and demonstrate the first case of lepton number violation.