Speaker
Description
Neutrinoless double beta decay ($0\nu\beta\beta$) is a hypothetical, lepton-number-violating process which, if observed, would confirm the Majorana nature of the neutrino. A proposed next-generation experiment searching for this decay in liquid xenon (LXe) is nEXO, anticipated to deploy 5 tonnes of LXe enriched to 90% in the double beta decay ($2\nu\beta\beta$) isotope $^{136}$Xe, targeting a half-life sensitivity beyond 10$^{28}$ years. A unique possibility with experiments such as nEXO is the possibility to access the detector volume to probe for the presence of the $^{136}$Ba daughter produced in a candidate decay. This technique, referred to as barium tagging, will provide confirmation of $0\nu\beta\beta$ on an event-by-event basis, reducing backgrounds down to the Standard Model-allowed $2\nu\beta\beta$ channel.
We present a summary of the Ba-tagging scheme being initially developed as an upgrade path for the nEXO experiment, with a focus on the development of the ion extraction and identification system. The system includes an RF-only ion funnel for transporting the Ba$^+$ from a high-pressure xenon gas environment to vacuum environment where it can then be trapped. The trapped Ba$^+$ can subsequently be identified via laser fluorescence spectroscopy. The system also includes a multiple-reflection time-of-flight mass spectrometer to confirm the presence of $^{136}$Ba$^+$ and enable systematic studies of ion extraction and transport using other ion species.
We will describe the overall tagging scheme and operating principles, the status of the R&D efforts and the near-term goals towards realizing a complete demonstration of single-ion extraction from LXe. These efforts aim to benchmark the overall performance of this Ba-tagging scheme and quantify the overall gain in discovery reach through its implementation in next-generation liquid xenon neutrinoless double beta decay searches.