Barium Chemosensors with Dry-Phase Fluorescence for Neutrinoless Double Beta Decay

Abstract

The nature of the neutrino is one of the major open questions in experimental nuclear and particle physics. The most sensitive known method to establish the Majorana nature of the neutrino is detection of the ultra-rare process of neutrinoless double beta decay. However, identification of one or a handful of decay events within a large mass of candidate isotope, without obfuscation by backgrounds is a formidable experimental challenge. One hypothetical method for achieving ultra- low-background neutrinoless double beta decay sensitivity is the detection of single 136Ba ions produced in the decay of 136Xe (“barium tagging”). To implement such a method, a single-ion-sensitive barium detector must be developed and demonstrated in bulk liquid or dry gaseous xenon. This paper reports on the development of two families of dry-phase barium chemosensor molecules for use in high pressure xenon gas detectors, synthesized specifically for this purpose. One particularly promising candidate, an anthracene substituted aza-18-crown-6 ether, is shown to respond in the dry phase with almost no intrinsic background from the unchelated state, and to be amenable to barium sensing through fluorescence microscopy. This interdisciplinary advance, paired with earlier work demonstrating sensitivity to single barium ions in solution, opens a new path toward single ion detection in high pressure xenon gas.

Radiogenic backgrounds in the NEXT double beta decay experiment

“…In addition, the detector low-density and fine spatial granularity of the tracking readout provides an efficient identification of the topological signature characteristic of 0νββ [11,12]. Finally, this technology offers promising 136 Ba (daughter of 136 Xe) tagging capabilities [13,14]. The implementation of an effective 136 Ba-tagging would imply a background-free experiment.…”

Sensitivity of the NEXT experiment to Xe-124 double electron capture

“…The NEXT technology can be scaled up to 0νββ source masses in the tonne scale introducing several technological advancements already available [23,24]. The NEXT collaboration is also pursuing a more radical approach to a tonne-scale experiment based on the efficient detection of the Ba ++ ion produced in the 0νββ decay of 136 Xe using single-molecule fluorescence imaging (SMFI) [24][25][26][27][28][29].…”

Results and future plans of the NEXT double beta decay experiment

“…R&D towards a feasible method of detecting the presence of 136 Ba ions in the gas is underway in a multidisciplinary effort to understand Single Molecule Fluorescence Imaging (SMFI) as a means to detect Ba ++ ions in dry media and the related machinery required for this method to be used in a TPC [11,12,13].…”