Barium tagging for Enhanced Double Beta Decay search for Majorana Neutrinos

Neutrinoless double beta decay is forbidden by the Standard Model of elementary particles. The nEXO collaboration aims to observe ¹³⁶Xe neutrinoless double beta decay to ¹³⁶Ba, which would confirm that the neutrino is a Majorana particle. The use of single atom imaging to identify the daughter barium could enhance nEXO's sensitivity in the future. Capturing the Ba atom in a solid xenon matrix is part of the technique being developed. Ba daughters trapped in a xenon ice matrix would then be detected and counted by single atom imaging.

We have identified the 670 nm emission from Ba in solid xenon as being due to the 6s6p ³P₁ to 6s^{2 1}S₀ transition of Ba atoms trapped in single vacancy sites within the solid xenon matrix. The 670 nm fluorescence increases with temperature from 10K to 40 K. This opens the possibility of single Ba imaging at 40 K, as opposed to around 10 K for previous work.¹ An interesting property of solid xenon is that its density decreases dramatically below 40 K. We have found that thin (~0.5 µm) solid xenon deposits stay clear to 10 K despite this density change, but thick (~100 µm) solid xenon deposits crack below 40 K. Pictures will be presented. Being able to image single Ba atoms in solid xenon at 40 K through the 670 nm emission could be very important, as it would allow thick deposits in the Ba daughter extraction process.