Description
Double beta decay is a process whereby two neutrons simultaneously decay into protons, emitting two electrons. The 100 kg scale EXO-200 precisely measured these decays with the emission of two neutrinos ($^{136}$Xe $2\nu\beta\beta$), with a half-life to be $2.165 \pm 0.016(stat) \pm 0.059 (syst) \times 10^{21}$ years. If the neutrino is a Majorana fermion, double beta decays are also possible without the emission of any neutrinos. EXO-200 placed one of the most stringent lower limits on the $^{136}$Xe $0\nu\beta\beta$ decay half-life at $3.5 \times 10^{25}$ years. Multi-ton detectors like the 5t nEXO are planned with $\sim100$ times greater reach. nEXO's projected half-life sensitivity is $1.35 \times 10^{28}$ years. This is accomplished by stringent control of all sources of background, along with taking advantage of the rich energy and topological information and the exquisite self-shielding of a large time projection chamber (TPC) with scintillation light readout.
Future upgraded detectors could also observe the $^{136}$Ba ions resulting from $^{136}$Xe double beta decays (so-named barium tagging) and eliminate all background signals other than the $2\nu\beta\beta$ decay. The high efficiency detection of a single ion following a double beta decay event in a potentially multi-ton detector medium is a challenging task. One proposed scheme is to extract $^{136}$Ba ions by flowing xenon through a small capillary for transport to subsequent stages of detection. Progress at Carleton University on the development of a capillary-based probe for individual ion extraction from liquid xenon will be presented, along with details of the experimental apparatus and the simulations of each step of the extraction.
| Collaboration | nEXO Collaboration |
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