Speaker
Description
Detection of neutrinoless double-beta decay ($0\nu\beta\beta$) would be an evidence of Majorana nature of neutrino, which clue on the extremely light neutrino mass and the matter dominant universe.
The KamLAND-Zen experiment started a search for $0\nu\beta\beta$ of $^{136}$Xe nuclei in 2011 (KamLAND-Zen400). The experiment was upgraded in 2019 by double amount of xenon nuclei and a tenfold reduction in uranium and thorium contamination (KamLAND-Zen 800). In addition, lots of new analytical technics including particle identification with neural network have been developed.
A combined analysis of the KamLAND-Zen 400 and 800 dataset yields a lower limit of the half life of $0\nu\beta\beta$: $T^{0\nu\beta\beta}_{1/2}=2.3\times 10^{26}$ years at 90% confidence level, which corresponds to the most strong upper limit on the effective Majorana neutrino mass of 36--156 meV with different nuclear matrix elements. This experiment achieved the first search of $0\nu\beta\beta$ in the inverted neutrino mass hierarchy region.
published article : https://doi.org/10.1103/PhysRevLett.130.051801
