KamLAND is marked by the ability to detect anti-neutrino signals at 1,000
ton of ultra-pure liquid scintillator. In 2009 the KamLAND collaboration
started a campaign to purify the liquid scintillator and ultimately achieved
a twentyfold reduction of 210Po, the dominant background in the prompt
energy region below 3.0 MeV. This reduction give a better
signal-to-background ratio for the geo-neutrino flux estimation and enhances
sensitivity to reactor neutrino oscillation below 2.6 MeV. Last year, we
presented new knowledges concerning anti-neutrino studies covering reactor
anti-neutrinos, geo anti-neutrinos and extraterrestrial anti-neutrinos.
Observation of neutrinoless double-beta decay would definitively establish
the Majorana nature of the neutrino, and provide information on the absolute
neutrino mass scale. KamLAND-Zen double-beta decay experiment is a
modification of the existing KamLAND detector carried out in the summer of
2011. The double-beta source/detector us 13 tons of Xe-loaded liquid
scintillator contained in a 3.08-m-diameter spherical inner balloon. We
measure two-neutrino double-beta decay half-life of 136Xe with high
statistics, and a lower limit for the neutrinoless double-beta decay
half-life is a factor 5 improvement over the previous limit.
In this talk, I will present overview of neutrino physics with KamLAND, and
status and future prospects of KamLAND-Zen.