SNOLAB Experiment: NEXO
NEXO is searching for the neutrinoless double beta decay of 136Xe.
A 200 kg prototype detector in the WIPP facility in New Mexico measured the related two-neutrino double beta decay of xenon for the first time and with the highest precision of any two-neutrino decay rate. This detector also demonstrated that the neutrinoless double beta decay rate was significantly smaller than had been previously claimed.
The EXO group is now designing a detector employing 5 tonnes of enriched xenon (NEXO) that will offer unparalleled sensitivity to neutrinoless double beta decay. The experiment will be a major undertaking with the xenon isotope alone costing some $50M. Such projects are feasible only when a collaborative global approach is taken. The collaboration proposes to install NEXO at SNOLAB. The development of advanced photodetectors would benefit NEXO greatly.
Strong scientific and technical support from CPARC, and substantial Canadian leadership, will enhance the prospects of this truly global-scale initiative becoming reality. One technical innovation with strong Canadian leadership is the development of techniques to tag individual Ba atoms produced in the double beta decay of xenon. A concept for this was developed at Carleton in which the Ba++ ions would be extracted into vacuum, converted to Ba+ which is an ion readily identified by laser fluorescence as being 136Ba, the ββ-decay daughter of 136Xe.
The expertise of the McGill and TRIUMF groups with RF-funneling and ion trapping will be essential to advance this technology, while the Carleton team continues to develop efficient techniques to effect the charge conversion and systems for the clean identification of the Ba ion. Meanwhile at Laurentian, techniques for meeting the extremely demanding radioactivity limits are refined, utilizing the special expertise and techniques developed for SNO. The University of Sherbrooke, very active in the development of the SiPM technology discussed below, has just joined the NEXO collaboration.