Experimental updates on development of accelerator-driven ion source at TRIUMF to benchmark Ba-tagging techniques for future neutrinoless double beta decay searches

Abstract

Neutrinoless double beta decay ($0νββ$) could provide a way to probe physics beyond the Standard Model of particle physics. The proposed nEXO experiment aims to search for $0νββ$ in $^{136}$Xe using a tonne-scale liquid xenon (LXe) time projection chamber. The projected half-life sensitivity for nEXO for 10 years of livetime is $>$10$^{28}$ years. Efforts are ongoing to further suppress backgrounds and increase the experiment's sensitivity. One approach pursued is Ba-tagging, which entails extracting and identifying the daughter nuclide from the $ββ$-decay of $^{136}$Xe, $^{136}$Ba. Once successful, this technique has the potential to separate background events from true $ββ$ events. While different extraction and identification methods are being investigated by different groups, a Ba-ion source is required for testing, quantifying and optimizing them. An accelerator-driven ion source is currently being developed at TRIUMF, where radioactive ions will be be injected into and stopped in an LXe volume, collected electrostatically and detected using $γ$ spectroscopy. In this contribution, an experimental status update on the commissioning of this Ba-ion source at TRIUMF is provided.