Tagging long-lived radioactive isotopes produced through cosmic-ray muon spallation in KamLAND

The most stringent limit on the neutrino less double beta decay half-life of ¹³⁶Xe is set by KamLAND-Zen at T1/2 > 2.3 × 10²⁶ yr. The experiment’s sensitivity is limited by long-lived radioactive isotopes produced from muon spallation of xenon nuclei in the xenon-doped liquid scintillator. The long lifetimes of the isotopes, typically up to several days, challenge the creation of an efficient tagging method, currently achieving only 42 ± 8.8%. We summarise the tagging techniques for both light and heavy spallation isotopes employed in KamLAND-Zen, and highlight the critical role of FLUKA simulations in developing new veto strategies.