Search for neutrinoless quadruple beta decay of Xe-136 in XMASS-I

Abstract

A search for the neutrinoless quadruple beta decay of Xe-136 was conducted with the liquid-xenon detector XMASS-I using 327 kg x800.0 days of the exposure. The pulse shape discrimination based on the scintillation decay time constant which distinguishes gamma-rays including the signal and beta-rays was used to enhance the search sensitivity. No significant signal excess was observed from the energy spectrum fitting with precise background evaluation, and we set a lower limit of the half life of 3.7 x 10(24) years at 90% confidence level. This is the first experimental constraint of the neutrinoless quadruple beta decay of Xe-136. (C) 2022 The Author(s). Published by Elsevier B.V.