nEXO is a proposed experiment to search for the neutrino-less double beta decay (0νββ) of 136Xe in a tonne-scale liquid xenon time projection chamber (TPC) . The nEXO TPC will be equipped with charge ...collection tiles to form the anode. In this work, the charge reconstruction performance of this anode design is studied with a dedicated simulation package. A multi-variate method and a deep neural network are developed to distinguish simulated 0νββ signals from backgrounds arising from trace levels of natural radioactivity in the detector materials. These simulations indicate that the nEXO TPC with charge-collection tiles shows promising capability to discriminate the 0νββ signal from backgrounds. The estimated half-life sensitivity for 0νββ decay is improved by ∼20(32)% with the multi-variate (deep neural network) methods considered here, relative to the sensitivity estimated in the nEXO pre-conceptual design report.
Cosmogenic backgrounds to 0νββ in EXO-200 Albert, J.B.; Auty, D.J.; Barbeau, P.S. ...
Journal of cosmology and astroparticle physics,
04/2016, Letnik:
2016, Številka:
4
Journal Article
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As neutrinoless double-beta decay experiments become more sensitive and intrinsic radioactivity in detector materials is reduced, previously minor contributions to the background must be understood ...and eliminated. With this in mind, cosmogenic backgrounds have been studied with the EXO-200 experiment. Using the EXO-200 TPC, the muon flux (through a flat horizontal surface) underground at the Waste Isolation Pilot Plant (WIPP) has been measured to be $Φ$ = 4.07±0.14 (sys)±0.03 (stat)×10-7 cm-2 s-1, with a vertical intensity of $I_v$ = 2.97+0.14-0.13 (sys) ± 0.02 (stat) × 10-7 cm-2 s-1 sr-1. Simulations of muon-induced backgrounds identified several potential cosmogenic radionuclides, though only 137Xe is a significant background for the 136Xe $0νββ$ search with EXO-200. Muon-induced neutron backgrounds were measured using $γ$-rays from neutron capture on the detector materials. This provided a measurement of 137Xe yield, and a test of the accuracy of the neutron production and transport simulations. The independently measured rates of 136Xe neutron capture and of 137Xe decay agree within uncertainties. Geant4 and FLUKA simulations were performed to estimate neutron capture rates, and these estimates agreed to within ~ 40% or better with measurements. The ability to identify 136Xe($n,γ$) events will allow for rejection of 137Xe backgrounds in future $0νββ$ analyses.
We study a possible calibration technique for the nEXOexperiment using a 127Xe electron capture source. nEXO is anext-generation search for neutrinoless double beta decay(0νββ) that will use a ...5-tonne, monolithic liquid xenontime projection chamber (TPC). The xenon, used both as source anddetection medium, will be enriched to 90% in 136Xe. Tooptimize the event reconstruction and energy resolution,calibrations are needed to map the position- and time-dependentdetector response. The 36.3 day half-life of 127Xe and itssmall Q-value compared to that of 136Xe 0νββ would allow a small activity to be maintained continuously in thedetector during normal operations without introducing additionalbackgrounds, thereby enabling in-situ calibration andmonitoring of the detector response. In this work we describe aprocess for producing the source and preliminary experimentaltests. We then use simulations to project the precision with whichsuch a source could calibrate spatial corrections to the light andcharge response of the nEXO TPC.
Xenon purity analysis for EXO-200 via mass spectrometry Dobi, A.; Hall, C.; Slutsky, S. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
05/2012, Letnik:
675
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We describe purity measurements of the natural and enriched xenon stockpiles used by the EXO-200 double beta decay experiment based on a mass spectrometry technique. The sensitivity of the ...spectrometer is enhanced by several orders of magnitude by the presence of a liquid nitrogen cold trap, and many impurity species of interest can be detected at the level of one part-per-billion or better. We have used the technique to screen the EXO-200 xenon before, during, and after its use in our detector, and these measurements have proven useful. This is the first application of the cold trap mass spectrometry technique to an operating physics experiment.
We study a possible calibration technique for the nEXO experiment using a $^{127}$Xe electron capture source. nEXO is a next-generation search for neutrinoless double beta decay (0νββ) that will use ...a 5-tonne, monolithic liquid xenon time projection chamber (TPC). The xenon, used both as source and detection medium, will be enriched to 90% in $^{136}$Xe. To optimize the event reconstruction and energy resolution, calibrations are needed to map the position- and time-dependent detector response. The 36.3 day half-life of $^{127}$Xe and its small Q-value compared to that of $^{136}$Xe 0νββ would allow a small activity to be maintained continuously in the detector during normal operations without introducing additional backgrounds, thereby enabling in-situ calibration and monitoring of the detector response. In this work we describe a process for producing the source and preliminary experimental tests. We then use simulations to project the precision with which such a source could calibrate spatial corrections to the light and charge response of the nEXO TPC.
We have developed a new technique for inclusive reconstruction of the energy of B hadrons. The excellent efficiency and resolution of this technique allow us to make the most precise determination of ...the b -quark fragmentation function, using e{sup +}e{sup -}{yields}Z{sup 0} decays recorded in the SLAC Large Detector experiment. We compared our measurement with the predictions of a number of fragmentation models. We excluded several of these models and measured the average scaled energy of weakly decaying B hadrons to be <x{sub B}>=0.714{+-}0.005(stat ){+-}0.007(syst){+-}0.00 2 (model dependence). (c) 2000 The American Physical Society.
Searches for double beta decay of 134Xe were performed with EXO-200, a single-phase liquid xenon detector designed to search for neutrinoless double beta decay of 136Xe. Using an exposure of 29.6 kg ...· yr, the lower limits of T2νββ 1=2 > 8.7 × 1020 yr and T0νββ 1=2 > 1.1 × 1023 yr at 90% confidence level were derived, with corresponding half-life sensitivities of 1.2 × 1021 yr and 1.9 × 1023 yr. These limits exceed those in the literature for 134Xe, improving by factors of nearly 105 and 2 for the two antineutrino and neutrinoless modes, respectively.
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