Search for Neutrinoless Double-β Decay with the Complete EXO-200 Dataset

A search for neutrinoless double-β decay (0 ν β β ) in ¹³⁶Xe is performed with the full EXO-200 dataset using a deep neural network to discriminate between 0 ν β β 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 ¹³⁶Xe 0 ν β β 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 0 ν β β half-life sensitivity for this analysis is 5.0 ×10²⁵ yr with a total ¹³⁶Xe exposure of 234.1 kg yr. No statistically significant evidence for 0 ν β β is observed, leading to a lower limit on the 0 ν β β half-life of 3.5 ×10²⁵ yr at the 90% confidence level.