Search for Majoron-emitting modes of double-beta decay of $^{136}$Xe with EXO-200

TL;DR

This paper reports a search for Majoron-emitting double-beta decay modes of $^{136}$Xe using the EXO-200 detector, setting new limits on decay half-life and Majoron-neutrino coupling.

Contribution

First search for Majoron-emitting modes in $^{136}$Xe with EXO-200, establishing new half-life limits and coupling constraints.

Findings

Half-life > 1.2 x 10^{24} years at 90% C.L.

Constraint on Majoron-neutrino coupling: |<g^{M}_{ee}>| < (0.8-1.7) x 10^{-5}.

No evidence of Majoron-emitting decay modes found.

Abstract

EXO-200 is a single phase liquid xenon detector designed to search for neutrinoless double-beta decay of $^{136}$Xe. Here we report on a search for various Majoron-emitting modes based on 100 kg$\cdot$yr exposure of $^{136}$Xe. A lower limit of $T^{^{136}Xe}_{1/2} >1.2 \cdot 10^{24}$ yr at 90% C.L. on the half-life of the spectral index = 1 Majoron decay was obtained, corresponding to a constraint on the Majoron-neutrino coupling constant of $|< g^{M}_{ee} >|<$ (0.8-1.7)$\cdot$10$^{-5}$.