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

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 $T_{1/2}^{{}^{136}Xe}>1.2\cdot 10^{24}$ 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 $|<g_{ee}^M>|<$ (0.8-1.7)$\cdot$10${}^{-5}$.

Published in PRD. Version 2: Referee comments addressed, journal reference added