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

TL;DR

This study searched for Lorentz and CPT violation effects in double beta decay of xenon-136 using EXO-200, setting new limits on SME coefficients and marking the first experimental investigation of this kind.

Contribution

It provides the first experimental constraints on SME coefficients related to Lorentz and CPT violation in double beta decay.

Findings

No significant Lorentz-violating signals detected.

Established new limits on SME coefficients.

First experimental test of SME neutrino coupling in double beta decay.

Abstract

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