Single Molecule Fluorescence Imaging as a Technique for Barium Tagging in Neutrinoless Double Beta Decay

TL;DR

This paper proposes using Single Molecule Fluorescent Imaging (SMFI) to detect barium ions as a method for background rejection in neutrinoless double beta decay experiments, potentially enabling zero-background, ton-scale detectors.

Contribution

It introduces a novel application of SMFI for barium ion detection in high-pressure xenon gas, advancing background suppression techniques in neutrino physics.

Findings

Sensor achieves signal-to-background ratio of 85 in aqueous solution

Developed fiber-coupled system for remote Ba$^{++}$ detection

Next step is demonstrating chelation and fluorescence in xenon gas

Abstract

Background rejection is key to success for future neutrinoless double beta decay experiments. To achieve sensitivity to effective Majorana lifetimes of $\sim10^{28}$ years, backgrounds must be controlled to better than 0.1 count per ton per year, beyond the reach of any present technology. In this paper we propose a new method to identify the birth of the barium daughter ion in the neutrinoless double beta decay of $^{136}$Xe. The method adapts Single Molecule Fluorescent Imaging, a technique from biochemistry research with demonstrated single ion sensitivity. We explore possible SMFI dyes suitable for the problem of barium ion detection in high pressure xenon gas, and develop a fiber-coupled sensing system with which we can detect the presence of bulk Ba$^{++}$ ions remotely. We show that our sensor produces signal-to-background ratios as high as 85 in response to Ba$^{++}$ ions when operated in aqueous solution. We then describe the next stage of this R\&D program, which will be to demonstrate chelation and fluorescence in xenon gas. If a successful barium ion tag can be developed using SMFI adapted for high pressure xenon gas detectors, the first essentially zero background, ton-scale neutrinoless double beta decay technology could be realized.