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

J. B. Albert, G. Anton, I. Badhrees, P. S. Barbeau, R. Bayerlein, D. Beck, V. Belov, M. Breidenbach, T. Brunner, G. F. Cao, W. R. Cen, C. Chambers, B. Cleveland, M. Coon, A. Craycraft, W. Cree, T. Daniels, M. Danilov, S. J. Daugherty, J. Daughhetee, J. Davis, S. Delaquis, A. Der Mesrobian-Kabakian, R. DeVoe, T. Didberidze, J. Dilling, A. Dolgolenko, M. J. Dolinski, W. Fairbank Jr., J. Farine, S. Feyzbakhsh, P. Fierlinger, D. Fudenberg, R. Gornea, K. Graham, G. Gratta, C. Hall, E. V. Hansen, J. Hoessl, P. Hufschmidt, M. Hughes, A. Jamil, M. J. Jewell, A. Johnson, S. Johnston, A. Karelin, L. J. Kaufman, T. Koffas, S. Kravitz, R. Krücken, A. Kuchenkov, K. S. Kumar, Y. Lan, D. S. Leonard, G. S. Li, S. Li, C. Licciardi, Y. H. Lin, R. MacLellan, T. Michel, B. Mong, D. Moore, K. Murray, R. Nelson, O. Njoya, A. Odian, I. Ostrovskiy, A. Piepke, A. Pocar, F. Retière, P. C. Rowson, J. J. Russell, S. Schmidt, A. Schubert, D. Sinclair, V. Stekhanov, M. Tarka, T. Tolba, R. Tsang, P. Vogel, J. -L. Vuilleumier, M. Wagenpfeil, A. Waite, T. Walton, M. Weber, L. J. Wen, U. Wichoski, G. Wrede, L. Yang, Y. -R. Yen, O. Ya. Zeldovich, J. Zettlemoyer, T. Ziegler

Published 2017-07-27Version 1

Results from a search for neutrinoless double-beta decay $0\nu\beta\!\beta$ 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 $\sigma/E$=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 2-fold to $3.7 \cdot 10^{25}$ 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 $1.8\cdot10^{25}$ yr at the 90% confidence level.