Spectroscopy of Ba and Ba$^+$ deposits in solid xenon for barium tagging in nEXO

TL;DR

This paper reports spectroscopic studies of barium atoms and ions in solid xenon to advance barium tagging techniques for the nEXO double beta decay experiment, including spectra analysis, site identification, and imaging prospects.

Contribution

It provides new spectroscopic data on Ba and Ba$^+$ in solid xenon, identifies matrix sites and molecules, and discusses the potential for single-atom imaging in this medium.

Findings

Spectra of Ba and Ba$^+$ in solid xenon are characterized.

Identification of barium hydride molecules in the matrix.

Feasibility of imaging up to 10^4 Ba atoms and prospects for single-atom detection.

Abstract

Progress on a method of barium tagging for the nEXO double beta decay experiment is reported. Absorption and emission spectra for deposits of barium atoms and ions in solid xenon matrices are presented. Excitation spectra for prominent emission lines, temperature dependence and bleaching of the fluorescence reveal the existence of different matrix sites. A regular series of sharp lines observed in Ba$^+$ deposits is identified with some type of barium hydride molecule. Lower limits for the fluorescence quantum efficiency of the principal Ba emission transition are reported. Under current conditions, an image of $\le10^4$ Ba atoms can be obtained. Prospects for imaging single Ba atoms in solid xenon are discussed.