A New Method for Detecting Charged-Current Neutrino Interactions on $^{136}$Xe in KamLAND-Zen: Implications for Solar Neutrino Measurements and Fermionic Dark Matter Searches

Abstract

A 136 Xe nuclei capture electron neutrinos through charged-current (CC) interaction. This lead to an excited state of 136 Cs : 𝜈 e + 136 Xe → e − + 136 Cs (1 + ). This reaction can be used for low energy solar neutrino measurements and MeV scale mass fermionic dark matter searches. The recent observation of low-lying isomeric states in 136 Cs with lifetimes on the order of 100 ns implies that the CC interaction can be identified by a delayed-coincidence measurement in liquid scintillator detector. This technique involves detecting a prompt signal conposed of the electron and most of the de-excitation 𝛾-rays, followed by a delayed signal consisting of the remaining de-excitation 𝛾-rays with energies below 140 keV. KamLAND-Zen is an experiment designed to search for neutrinoless double-beta decay of 136 Xe. KamLAND-Zen uses organic liquid scintillators dissolving 750 kg of xenon (91% enriched in 136 Xe) and has the world's largest exposure to the CC reaction. We conducted a feasibility study of identifying the CC interaction in KamLAND-Zen.