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

Abstract

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.