A Search for Lorentz and CPT Violation with the Full EXO-200 Dataset

Neutrinoless double beta (0νββ) decay is currently one of the most compelling searches in particle physics. If found, it would imply the existence of Majorana fermions and lepton number violation, both new physics beyond the Standard Model. The EXO-200 experiment consisted of a time projection chamber (TPC) with 200 kg of enriched liquid xenon (LXe) optimized to search for 0νββ of ¹³⁶Xe. Data acquisition took place from 2011 to the end of 2018, with a total exposure of 234.1kg·yr. We found no statistically significant evidence for 0νββ, leading to a lower limit on the half-life of 3.5×10²⁵ yr at the 90% confidence level. In addition, the ultra-low background necessary for this search provides a unique opportunity to probe other exotic processes, such as Lorentz and CPT violation, predicted by the Standard Model extension (SME) framework. This presents itself in double beta decay as a spectral perturbation due to neutrino coupling with an SME Lorentz-violating tensor field. The first search for this process was published in 2016 using a subset of the EXO-200 dataset. In this talk, we will present the analysis and status of an updated search using the full EXO-200 dataset with lower energy thresholds and improved systematic uncertainties.