The Kamioka Liquid Scintillator Antineutrino Detector, or KamLAND, is a pioneering neutrino experiment located in the Kamioka Mozumi mine in Japan. It was designed primarily to investigate electron antineutrinos produced by nuclear reactors. KamLAND consists of a large spherical volume filled with ultra-pure liquid scintillator, surrounded by a dense array of photomultiplier tubes. When electron antineutrinos interact with the scintillator, they produce flashes of light, which are detected by the photomultiplier tubes. KamLAND's main objective is to study neutrino oscillations, a phenomenon where neutrinos change from one type to another as they travel through space, providing crucial insights into neutrino properties such as their masses and mixing angles.

The KamLAND-Zen experiment is an extension of the KamLAND project, specifically designed to search for a rare nuclear decay process known as neutrinoless double-beta decay (0νββ). In standard double-beta decay, two neutrons in an atomic nucleus simultaneously transform into two protons with the emission of two electrons and two electron antineutrinos. However, in neutrinoless double-beta decay, the emitted antineutrinos are not observed. The observation of this process would have profound implications for our understanding of neutrinos, suggesting that neutrinos and antineutrinos are the same particle (Majorana particles) and providing information about the absolute neutrino mass.

KamLAND-Zen employs the same large scintillator volume as KamLAND but incorporates additional isotopes, such as xenon, to enhance sensitivity to neutrinoless double-beta decay. The collaboration aims to detect this rare decay process, which, if observed, could revolutionize our understanding of fundamental particle physics and the nature of neutrinos. The results from KamLAND-Zen contribute to the global effort to determine the properties of neutrinos and address some of the most profound questions in particle physics.