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Barium-ion tagging for $^{136}$Xe double-beta decay studies with EXO

5 Jun 2014, 16:50
Veilingzaal (Beurs van Berlage)


Beurs van Berlage

Oral Experiments: 2c) Detectors for neutrino physics II.c Neutrino


Thomas Brunner (S)


The nature of the neutrino, i.e. whether it is a Dirac or Majorana particle, remains a mystery. Decay experiments that search for the lepton-number violating neutrino-less double decay ($0\nu\beta\beta$) are an experimental approach to answer this question. EXO-200 is one such experiment, searching for a $0\nu\beta\beta$ signal in the $\beta\beta$ decay of $^{136}$Xe to its daughter isotope $^{136}$Ba. This detector, located at the WIPP site in New Mexico, USA, contains ~200 kg liquid Xe enriched to ~80%. In order to further push sensitivity, it is necessary to suppress the background (currently dominated by gamma rays) and increase the mass of the parent isotope. A unique advantage of a Xe time-projection chamber (TPC) is the possibility to extract into vacuum and identify (to tag) Ba-daughter ions. This tagging possibility, combined with enough energy resolution to separate $0\nu\beta\beta$ from $2\nu\beta\beta$ decays, allows one to dramatically reduce the background of the measurement to virtually zero. EXO has started development of nEXO, a multi-ton scale TPC. In addition, Ba-tagging techniques, in both liquid and gas phase TPCs, are under development. In a liquid Xe TPC, the Ba ion will be extracted mechanically by a probe. In a high pressure (10 bar) gas Xe TPC, the Ba ion will be extracted into vacuum through a supersonic nozzle combined with an extraction RF-funnel. The current status of these Ba-tagging techniques will be presented and possible future developments will be discussed.

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