Results from a search for neutrinoless double-beta decay (0νββ) of ^{136}Xe are presented using the first year of data taken with the upgraded EXO-200 detector. Relative to previous searches by ...EXO-200, the energy resolution of the detector has been improved to σ/E=1.23%, the electric field in the drift region has been raised by 50%, and a system to suppress radon in the volume between the cryostat and lead shielding has been implemented. In addition, analysis techniques that improve topological discrimination between 0νββ and background events have been developed. Incorporating these hardware and analysis improvements, the median 90% confidence level 0νββ half-life sensitivity after combining with the full data set acquired before the upgrade has increased twofold to 3.7×10^{25} yr. No statistically significant evidence for 0νββ is observed, leading to a lower limit on the 0νββ half-life of 1.8×10^{25} yr at the 90% confidence level.
We apply deep neural networks (DNN) to data from the EXO-200 experiment. In the studied cases, the DNN is able to reconstruct the relevant parameters—total energy and position—directly from raw ...digitized waveforms, with minimal exceptions. For the first time, the developed algorithms are evaluated on real detector calibration data. The accuracy of reconstruction either reaches or exceeds what was achieved by the conventional approaches developed by EXO-200 over the course of the experiment. Most existing DNN approaches to event reconstruction and classification in particle physics are trained on Monte Carlo simulated events. Such algorithms are inherently limited by the accuracy of the simulation. We describe a unique approach that, in an experiment such as EXO-200, allows to successfully perform certain reconstruction and analysis tasks by training the network on waveforms from experimental data, either reducing or eliminating the reliance on the Monte Carlo.
Abstract
The nEXO neutrinoless double beta (0νββ) decay experiment is designed to use a time projection chamber and 5000 kg of isotopically enriched liquid xenon to search for the decay in 136Xe. ...Progress in the detector design, paired with higher fidelity in its simulation and an advanced data analysis, based on the one used for the final results of EXO-200, produce a sensitivity prediction that exceeds the half-life of 1028 years. Specifically, improvements have been made in the understanding of production of scintillation photons and charge as well as of their transport and reconstruction in the detector. The more detailed knowledge of the detector construction has been paired with more assays for trace radioactivity in different materials. In particular, the use of custom electroformed copper is now incorporated in the design, leading to a substantial reduction in backgrounds from the intrinsic radioactivity of detector materials. Furthermore, a number of assumptions from previous sensitivity projections have gained further support from interim work validating the nEXO experiment concept. Together these improvements and updates suggest that the nEXO experiment will reach a half-life sensitivity of 1.35 × 1028 yr at 90% confidence level in 10 years of data taking, covering the parameter space associated with the inverted neutrino mass ordering, along with a significant portion of the parameter space for the normal ordering scenario, for almost all nuclear matrix elements. The effects of backgrounds deviating from the nominal values used for the projections are also illustrated, concluding that the nEXO design is robust against a number of imperfections of the model.
The Enriched Xenon Observatory (EXO) will search for double beta decays of
136Xe. We report the results of a systematic study of trace concentrations of radioactive impurities in a wide range of raw ...materials and finished parts considered for use in the construction of EXO-200, the first stage of the EXO experimental program. Analysis techniques employed, and described here, include direct gamma counting, alpha counting, neutron activation analysis, and high-sensitivity mass spectrometry.
Mixed Self-Assembled Monolayers in Chemical Separations Wirth, Mary J.; R. W. Peter Fairbank; Fatunmbi, Hafeez O.
Science (American Association for the Advancement of Science),
01/1997, Letnik:
275, Številka:
5296
Journal Article
Recenzirano
Chemical separations of many biomolecules and pharmaceuticals are limited by their electrostatic interaction with the surfaces of the separation medium. Mixed self-assembled monolayers of octadecyl ...and methyl chains organize into a dense, two-dimensionally cross-linked network over the chromatographic silica surface to reduce acid dissociation of the surface silanols. Molecular models predict that two-dimensional cross-linking is sterically possible for pure methylsiloxane monolayers, silicon-29 nuclear magnetic resonance measurements show that cross-linking predominates for mixed monolayers of primarily methylsiloxane, and chromatographic measurements confirm that electrostatic interactions are reduced when the monolayer is primarily methylsiloxane. Chromatographic separation of genetic variants of a highly charged protein, cytochrome c, demonstrates the promise of self-assembled monolayers in separations of biomolecules.
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
Recenzirano
Odprti dostop
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.
Characterization of large area APDs for the EXO-200 detector Neilson, R.; LePort, F.; Pocar, A. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
09/2009, Letnik:
608, Številka:
1
Journal Article
Recenzirano
Odprti dostop
Enriched Xenon Observatory (EXO)-200 uses 468 large area avalanche photodiodes (LAAPDs) for detection of scintillation light in an ultra-low-background liquid xenon (LXe) detector. We describe ...initial measurements of dark noise, gain and response to xenon scintillation light of LAAPDs at temperatures from room temperature to 169
K—the temperature of liquid xenon. We also describe the individual characterization of more than 800 LAAPDs for selective installation in the EXO-200 detector.
The mobility of alkaline earth ions, Mg+, Ca+, Sr+ and Ba+, in liquid xenon is measured for the first time. The mobility of Tl+ is also determined for comparison with a measurement by other ...researchers. The Atkins cluster model for positive ions in non-polar liquids, based on the electrostriction effect, gives general agreement with the magnitude of the mobility values. This is some evidence that the positive ions form a snowball rather than a bubble structure in liquid xenon. However, the temperature dependence of the mobility does not match well with the Atkins theory, so there are still open theoretical questions on the nature of the environment of alkaline earth ions in liquid xenon. The lower mobility of Mg+ and Ba+ may be explained by a better size match to interstitial and substitutional sites, respectively, in solid Xe. These measurements are motivated by the development of a new technique to search for neutrino masses through 0nubetabeta decay of 136Xe. A key component of one version of the proposed experiment is tagging of 136Ba+ daughter ions in liquid 136Xe by laser-induced fluorescence.
Epidemiology of child traumatic stress Fairbank, John A.; Fairbank, Doreen W.
Current psychiatry reports,
08/2009, Letnik:
11, Številka:
4
Journal Article
Recenzirano
In this article, we present an update on epidemiologic research that addresses the scope and impact of children’s exposure to traumatic events in daily living, as well as under special circumstances, ...such as natural disasters. Toward this end, we provide an overview of the findings of key selected studies that estimate the prevalence of children’s exposure to trauma and associated developmental, functional, mental, and physical health problems. Over the past few years, epidemiologic research on child traumatic stress has demonstrated that children’s exposure to traumatic events is more common than once thought and that children exposed to multiple traumatic events are at a substantially greater risk for a wide range of adverse mental and physical health problems than children who have not suffered cumulative traumatic experiences. These findings have important implications for the provision of mental health and medical services to children and adolescents who have experienced child traumatic stress.
A search for neutrinoless double-β decay (0νββ) in Xe136 is performed with the full EXO-200 dataset using a deep neural network to discriminate between 0νββ and background events. Relative to ...previous analyses, the signal detection efficiency has been raised from 80.8% to 96.4±3.0%, and the energy resolution of the detector at the Q value of Xe136 0νββ has been improved from σ/E=1.23% to 1.15±0.02% with the upgraded detector. Accounting for the new data, the median 90% confidence level 0νββ half-life sensitivity for this analysis is 5.0×1025 yr with a total Xe136 exposure of 234.1 kg yr. No statistically significant evidence for 0νββ is observed, leading to a lower limit on the 0νββ half-life of 3.5×1025 yr at the 90% confidence level.
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