43 research outputs found
Measurement of the Spectral Shape of the beta-decay of 137Xe to the Ground State of 137Cs in EXO-200 and Comparison with Theory
We report on a comparison between the theoretically predicted and
experimentally measured spectra of the first-forbidden non-unique -decay
transition ^{137}\textrm{Xe}(7/2^-)\to\,^{137}\textrm{Cs}(7/2^+). The
experimental data were acquired by the EXO-200 experiment during a deployment
of an AmBe neutron source. The ultra-low background environment of EXO-200,
together with dedicated source deployment and analysis procedures, allowed for
collection of a pure sample of the decays, with an estimated
signal-to-background ratio of more than 99-to-1 in the energy range from 1075
to 4175 keV. In addition to providing a rare and accurate measurement of the
first-forbidden non-unique -decay shape, this work constitutes a novel
test of the calculated electron spectral shapes in the context of the reactor
antineutrino anomaly and spectral bump.Comment: Version as accepted by PR
Generative Adversarial Networks for Scintillation Signal Simulation in EXO-200
Generative Adversarial Networks trained on samples of simulated or actual
events have been proposed as a way of generating large simulated datasets at a
reduced computational cost. In this work, a novel approach to perform the
simulation of photodetector signals from the time projection chamber of the
EXO-200 experiment is demonstrated. The method is based on a Wasserstein
Generative Adversarial Network - a deep learning technique allowing for
implicit non-parametric estimation of the population distribution for a given
set of objects. Our network is trained on real calibration data using raw
scintillation waveforms as input. We find that it is able to produce
high-quality simulated waveforms an order of magnitude faster than the
traditional simulation approach and, importantly, generalize from the training
sample and discern salient high-level features of the data. In particular, the
network correctly deduces position dependency of scintillation light response
in the detector and correctly recognizes dead photodetector channels. The
network output is then integrated into the EXO-200 analysis framework to show
that the standard EXO-200 reconstruction routine processes the simulated
waveforms to produce energy distributions comparable to that of real waveforms.
Finally, the remaining discrepancies and potential ways to improve the approach
further are highlighted.Comment: 20 pages, 10 figure
Measurement of the Spectral Shape of the β-Decay of ¹³⁷Xe to the Ground State of ¹³⁷Cs in EXO-200 and Comparison with Theory
We report on a comparison between the theoretically predicted and experimentally measured spectra of the first-forbidden nonunique β-decay transition ¹³⁷Xe(7/2⁻)→¹³⁷Cs(7/2⁺). The experimental data were acquired by the EXO-200 experiment during a deployment of an AmBe neutron source. The ultralow background environment of EXO-200, together with dedicated source deployment and analysis procedures, allowed for collection of a pure sample of the decays, with an estimated signal to background ratio of more than 99 to 1 in the energy range from 1075 to 4175 keV. In addition to providing a rare and accurate measurement of the first-forbidden nonunique β-decay shape, this work constitutes a novel test of the calculated electron spectral shapes in the context of the reactor antineutrino anomaly and spectral bump
An integrated online radioassay data storage and analytics tool for nEXO
Large-scale low-background detectors are increasingly used in rare-event
searches as experimental collaborations push for enhanced sensitivity. However,
building such detectors, in practice, creates an abundance of radioassay data
especially during the conceptual phase of an experiment when hundreds of
materials are screened for radiopurity. A tool is needed to manage and make use
of the radioassay screening data to quantitatively assess detector design
options. We have developed a Materials Database Application for the nEXO
experiment to serve this purpose. This paper describes this database, explains
how it functions, and discusses how it streamlines the design of the
experiment
Measurement of the scintillation and ionization response of liquid xenon at MeV energies in the EXO-200 experiment
Liquid xenon (LXe) is employed in a number of current and future detectors
for rare event searches. We use the EXO-200 experimental data to measure the
absolute scintillation and ionization yields generated by interactions
from Th (2615~keV), Ra (1764~keV) and Co (1332~keV and
1173~keV) calibration sources, over a range of electric fields. The -value
that defines the recombination-independent energy scale is measured to be
~(syst.)~~(stat.) eV. These data are also used to
measure the recombination fluctuations in the number of electrons and photons
produced by the calibration sources at the MeV-scale, which deviate from
extrapolations of lower-energy data. Additionally, a semi-empirical model for
the energy resolution of the detector is developed, which is used to constrain
the recombination efficiency, i.e., the fraction of recombined electrons that
result in the emission of a detectable photon. Detailed measurements of the
absolute charge and light yields for MeV-scale electron recoils are important
for predicting the performance of future neutrinoless double beta decay
detectors
Performance of novel VUV-sensitive Silicon Photo-Multipliers for nEXO
Liquid xenon time projection chambers are promising detectors to search for
neutrinoless double beta decay (0), due to their response
uniformity, monolithic sensitive volume, scalability to large target masses,
and suitability for extremely low background operations. The nEXO collaboration
has designed a tonne-scale time projection chamber that aims to search for
0 of \ce{^{136}Xe} with projected half-life sensitivity of
~yr. To reach this sensitivity, the design goal for nEXO is
1\% energy resolution at the decay -value (~keV).
Reaching this resolution requires the efficient collection of both the
ionization and scintillation produced in the detector. The nEXO design employs
Silicon Photo-Multipliers (SiPMs) to detect the vacuum ultra-violet, 175 nm
scintillation light of liquid xenon. This paper reports on the characterization
of the newest vacuum ultra-violet sensitive Fondazione Bruno Kessler VUVHD3
SiPMs specifically designed for nEXO, as well as new measurements on new test
samples of previously characterised Hamamatsu VUV4 Multi Pixel Photon Counters
(MPPCs). Various SiPM and MPPC parameters, such as dark noise, gain, direct
crosstalk, correlated avalanches and photon detection efficiency were measured
as a function of the applied over voltage and wavelength at liquid xenon
temperature (163~K). The results from this study are used to provide updated
estimates of the achievable energy resolution at the decay -value for the
nEXO design