Simulation study of cosmic-ray muon backgrounds for KamLAND-Zen experiment

Neutrino is a major candidate of Majorana particle and the neutrinoless double beta (0v2β) decay is the key physics to prove it. In 2019, KamLAND-Zen experiment have started data taking to search for 0v2β decay with 745 kg of 136Xe as the source. The sensitivity is restricted by the statistics of backgrounds and the most critical ones are induced by spallation reactions of cosmic-ray muons. Physics process and statistics are studied with FLUKA which is widely used simulation tool. The most critical background is the decay of 10C, while FLUKA predicts that heavy isotopes such as 137Xe can be a potential background. We apply delayed coincidence method to quantify those backgrounds and also have been developing new tools focused on space and charge features, pulse shape discrimination and particle identification.