First search for Lorentz and CPT violation in double beta decay with EXO-200

A search for Lorentz- and CPT-violating signals in the double beta decay spectrum of Xe-136 has been performed using an exposure of 100 kg . yr with the EXO-200 detector. No significant evidence of the spectral modification due to isotropic Lorentz -violation was found, and a two-sided limit of -2.65 x 10(-5) GeV < (a)(of),(,3r) < 7.60 x 10(-6) GeV (90% C.L.) is placed on the relevant coefficient within the Standard -Model Extension (SME). This is the first experimental study of the effect of the SME-defined oscillation -free and momentum-independent neutrino coupling operator on the double beta decay process. © 2016 American Physical Society112111sciescopu

Search for 2 nu beta beta decay of Xe-136 to the 0(1)(+) excited state of Ba-136 with the EXO-200 liquid xenon detector

EXO-200 is a single phase liquid xenon detector designed to search for neutrinoless pp decay of Xe-136 to the ground state of Ba-136. We report here on a search for the two -neutrino pp decay of Xe-136 to the first 0+ excited state, 0(1)(+), of Ba-136 based on a 100 kg yr exposure of Xe-136. Using a specialized analysis employing a machine learning algorithm, we obtain a 90% CL half-life sensitivity of 1.7 x 10(24) yr. We find no statistically significant evidence for the 20P decay to the excited state resulting in a lower limit of Ti-1/2(7 nu) (0(+) -> 0(1)(+)) > 6.9 x10(23) yr at 90% CL. This observed limit is consistent with the estimated half-life of 2.5 x 10(25) yr.1551sciescopu

Investigation of radioactivity-induced backgrounds in EXO-200

The search for neutrinoless double-beta decay (0 nu beta beta) requires extremely low background and a good understanding of their sources and their influence on the rate in the region of parameter space relevant to the 0 nu beta beta signal. We report on studies of various beta and gamma backgrounds in the liquid-xenon-based EXO-200 0 nu beta beta experiment. With this work we try to better understand the location and strength of specific background sources and compare the conclusions to radioassay results taken before and during detector construction. Finally, we discuss the implications of these studies for EXO-200 as well as for the next-generation, tonne-scale nEXO detector117211scopu

An optimal energy estimator to reduce correlated noise for the EXO-200 light readout

The energy resolution of the EXO-200 detector is limited by electronics noise in the measurement of the scintillation response. Here we present a new technique to extract optimal scintillation energy measurements for signals split across multiple channels in the presence of correlated noise. The implementation of these techniques improves the energy resolution of the detector at the neutrinoless double beta decay Q-value from [1.9641 +/- 0.0039]% to [1.5820 +/- 0.0044]%. (c) 2016 IOP Publishing Ltd and Sissa Medialab srl511sciescopu

Measurements of the ion fraction and mobility of alpha- and beta-decay products in liquid xenon using the EXO-200 detector

Alpha decays in the EXO-200 detector are used to measure the fraction of charged Po-218 and Bi-214 daughters created from alpha and beta decays, respectively. Rn-222 alpha decays in liquid xenon (LXe) are found to produce Po-218(+) ions 50.3 +/- 3.0% of the time, while the remainder of the Po-218 atoms are neutral. The fraction of Bi-214(+) from Pb-214 beta decays in LXe is found to be 76.4 +/- 5.7%, inferred from the relative rates of Po-218 and Po-214 alpha decays in the LXe. The average velocity of 218Po ions is observed to decrease for longer drift times. Initially the ions have a mobility of 0.390 +/- 0.006 cm(2) /(kVs), and at long drift times the mobility is 0.219 +/- 0.004 cm(2) /(kVs). Time constants associated with the change in mobility during drift of the Po-218(+) ions are found to be proportional to the electron lifetime in the LXe161811Nsciescopu

Deep neural networks for energy and position reconstruction in EXO-200

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. (c) 2018 IOP Publishing Ltd and Sissa Mediala

Search for Neutrinoless Double-Beta Decay with the Upgraded EXO-200 Detector

Results from a search for neutrinoless double-beta decay (0 nu beta beta) of Xe-136 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 sigma/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 0 nu beta beta and background events have been developed. Incorporating these hardware and analysis improvements, the median 90% confidence level 0 nu beta beta half-life sensitivity after combining with the full data set acquired before the upgrade has increased twofold to 3.7 x 10(25) yr. No statistically significant evidence for 0 nu beta beta is observed, leading to a lower limit on the 0 nu beta beta half-life of 1.8 x 10(25) yr at the 90% confidence level. Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Funded by SCOAP3.151

Search for nucleon decays with EXO-200

A search for instability of nucleons bound in Xe136 nuclei is reported with 223 kg·yr exposure of Xe136 in the EXO-200 experiment. Lifetime limits of 3.3×1023 and 1.9×1023 yr are established for nucleon decay to Sb133 and Te133, respectively. These are the most stringent to date, exceeding the prior decay limits by a factor of 9 and 7, respectively