Grant: Subatomic Physics Envelope - Project

This application seeks support for a three-year grant for the development of an innovative background reduction technique and its application to a repurposed tonne-scale particle detector for the search of neutrinoless double beta decay with Xe-136. The Canadian Collaboration on Ba Ion Tagging is composed of EXO collaboration members working on the development of the Ba ion tagging, and other Canadian researchers with expertise in low background techniques and the operation of tonne-scale particle detectors. During this grant period, the Ba ion tagging technique would be tested and optimized in preparation of future stages. The integration of the Ba ion tagging apparatus to a tonne-scale detector would be studied conceptually, with the construction and operation planned for future grant requests. Neutrino oscillation experiments have demonstrated that neutrinos have a finite mass, we know from cosmological bounds that neutrino masses are at least six orders of magnitude smaller than that of the electron. Neutrinos carry only weak charge and, therefore, could be their own anti-particle, a.k.a. Majorana particles. This opens the door to the possibility of having lepton number violating processes which could shed light on the physics beyond the standard model and explain the matter dominated universe we are witnessing today. Experimentally, neutrinoless double beta (0nbb) decay experiments are excellent probes for the Majorana nature of the neutrino, in addition to enabling the determination of the effective neutrino mass. The natural residual radioactivity represents a considerable challenge for 0nbb decay experiments, and tremendous efforts are made to screen all the materials employed to build detectors, as well as to assemble and operate those deep underground and in an ultra radiopure environment. Ideally, such experiments would be best conducted with a detector that has no radioactive background at all. Practically, this aim can only be achieved by exploiting signal event tagging. The decay of Xe-136 produces a Ba-136 ion. The scheme of attempting the collection, detection and identification of this ion is designated as Ba ion tagging. The residual radioactive background can be completely rejected by detecting and tagging the ba-136 ion. Extracting a single-ion from a tonne-scale detector, and then detecting it efficiently, is very challenging but not impossible. We are proposing a synergistic Canadian R&D program to develop and integrate all the components needed for the application of efficient Ba ion tagging to a tonne-scale LXe detector. The proposed project benefits from the existence of a significant amount of hardware infrastructure and expertise at three Canadian institutions. Over the three years of this grant proposal, the ion transport R&D will be finalized and the conceptual design of a capillary-based ion extraction probe concluded.