Center for Underground Physics

KamLAND-Zen is an experiment searching for neutrinoless double-beta 
decay (0νββ) in Xe-136 using the large liquid scintillator detector 
KamLAND. The latest experimental phase, KamLAND-Zen 800, collected 
physics data from May 2019 to January 2024.
In this talk, I will present the latest KamLAND-Zen results based on the 
complete dataset. A major challenge in this search arises from long-
lived radioactive isotopes produced by muon spallation on xenon. The 
presentation will cover the detector configuration, background rejection 
and model including study of xenon spallation products, and the limit on 
the effective Majorana mass.
We are currently carrying out a detector upgrade as part of the KamLAND2 
project, aiming to reduce backgrounds and improve sensitivity. I will 
conclude with the current status of the on-site work for the upgrade.