Search for Majorana Neutrinos with 1 Ton-Year Exposure Data of KamLAND-Zen

KamLAND-Zen experiment is searching for neutrinoless double-beta decay of \(^{136}\) Xe using a liquid scintillator detector at the Kamioka Observatory in Japan. The KamLAND-Zen detector contains 745kg of enriched xenon and we have been taking data since January 2nd, 2019. This paper reports the 1st result from the KamLAND-Zen experiment at 970 kg-yr exposure. Statistically significant excess was not observed in our region of interest (2.35 \(<E_ we="" set="" a="" limit="" on="" the="" neutrinoless="" double-beta="" decay="" half-life="" _T__1="" _="">2.3\times 10^{26}\)  yr at 90% C.L. Corresponding upper limits on the effective Majorana neutrino mass is \(\langle m_{\beta \beta }\rangle <(36-156)\)  meV using commonly adopted nuclear matrix element calculations.