‘Searching for a needle in a haystack;’ A Ba-tagging approach for an upgraded nEXO experiment

nEXO is a proposed experiment that will search for neutrinoless double-beta decay (0 ν β β ) in 5-tonnes of liquid xenon (LXe), isotopically enriched in 136Xe . A technique called Ba-tagging is being developed as a potential future upgrade for nEXO to detect the 136Xe double-beta decay daughter isotope, 136Ba . An efficient Ba-tagging technique has the potential to boost nEXO’s 0 ν β β sensitivity by essentially suppressing non-double-beta decay background events. A conceptual approach for the extraction from the detector volume, trapping, and identification of a single Ba ion from 5 tonnes of LXe is presented, along with initial results from the commissioning of one of its subsystems, a quadrupole mass filter.