First Search for Lorentz and CPT Violation in Double Beta Decay with EXO-200

This proceedings contribution reports the first experimental search for Lorentz- and CPT-violating signals specifically studying the effect of the Standard-Model Extension (SME) oscillation-free momentum-independent neutrino coupling operator in the double beta decay process. The search has been performed using an exposure of 100 kg yr of ${}^{136}$Xe with the EXO-200 detector. No significant evidence of the spectral modification due to isotropic Lorentz violation was found. A two-sided limit of $-2.65\times {10}^{-5}$ GeV $<$ ${\mathring{a}}_{\mathrm{o}\mathrm{f}}^{(3)}$ $<7.60\times {10}^{-6}$ GeV (90% C.L.) is placed on the relevant coefficient within the SME.