A. Gando

We present an improved search for neutrinoless double-beta (0νββ) decay of ^{136}Xe in the KamLAND-Zen experiment. Owing to purification of the xenon-loaded liquid scintillator, we achieved a significant reduction of the ^{110m}Ag contaminant identified in previous searches. Combining the results from the first and second phase, we obtain a lower limit for the 0νββ decay half-life of T_{1/2}^{0ν}>1.07×10^{26} yr at 90% C.L., an almost sixfold improvement over previous limits. Using commonly adop

We present results from the first phase of the KamLAND-Zen double-beta decay experiment, corresponding to an exposure of 89.5 kg yr of (136)Xe. We obtain a lower limit for the neutrinoless double-beta decay half-life of T(1/2)(0ν)>1.9×10(25) yr at 90% C.L. The combined results from KamLAND-Zen and EXO-200 give T(1/2)(0ν)>3.4×10(25) yr at 90% C.L., which corresponds to a Majorana neutrino mass limit of <m(ββ)> <(120-250) meV based on a representative range of available matrix element calculations

The recent long-term shutdown of Japanese nuclear reactors has resulted in a significantly reduced reactor ${\overline{\ensuremath{\nu}}}_{e}$ flux at KamLAND. This running condition provides a unique opportunity to confirm and constrain backgrounds for the reactor ${\overline{\ensuremath{\nu}}}_{e}$ oscillation analysis. The data set also has improved sensitivity for other ${\overline{\ensuremath{\nu}}}_{e}$ signals, in particular ${\overline{\ensuremath{\nu}}}_{e}$'s produced in $\ensuremath{\

We present new constraints on the neutrino oscillation parameters $\ensuremath{\Delta}{m}_{21}^{2}$, ${\ensuremath{\theta}}_{12}$, and ${\ensuremath{\theta}}_{13}$ from a three-flavor analysis of solar and KamLAND data. The KamLAND data set includes data acquired following a radiopurity upgrade and amounts to a total exposure of $3.49\ifmmode\times\else\texttimes\fi{}{10}^{32}$ target-proton-year. Under the assumption of $CPT$ invariance, a two-flavor analysis (${\ensuremath{\theta}}_{13}=0$) of

This corrects the article DOI: 10.1103/PhysRevLett.117.082503.

We present results from the KamLAND-Zen double-beta decay experiment based on an exposure of 77.6 days with 129 kg of ${}^{136}$Xe. The measured two-neutrino double-beta decay half-life of ${}^{136}$Xe is ${T}_{1/2}^{2\ensuremath{\nu}}=2.38\ifmmode\pm\else\textpm\fi{}0.02(\mathrm{stat})\ifmmode\pm\else\textpm\fi{}0.14(\mathrm{syst})\ifmmode\times\else\texttimes\fi{}{10}^{21}$ yr, consistent with a recent measurement by EXO-200. We also obtain a lower limit for the neutrinoless double-beta decay

We present the results of a search for extraterrestrial electron antineutrinos ( e 's) in the energy range 8.3 MeV < E e < 31.8 MeV using the KamLAND detector. In an exposure of 4.53 kton-year, we identify 25 candidate events. All of the candidate events can be attributed to background, most importantly neutral current atmospheric neutrino interactions, setting an upper limit on the probability of 8 B solar e 's converting into e 's at 5.3 10 -5 (90% CL), if we assume an undistorted e shape. Thi

We present limits on Majoron-emitting neutrinoless double-$\ensuremath{\beta}$ decay modes based on an exposure of 112.3 days with 125 kg of ${}^{136}$Xe. In particular, a lower limit on the ordinary (spectral index $n=1$) Majoron-emitting decay half-life of ${}^{136}$Xe is obtained as ${T}_{1/2}^{0\ensuremath{\nu}{\ensuremath{\chi}}^{0}}&gt;2.6\ifmmode\times\else\texttimes\fi{}{10}^{24}$ yr at 90$%$ C.L., a factor of five more stringent than previous limits. The corresponding upper limit on the

We report a measurement of the neutrino-electron elastic scattering rate of 862 keV $^{7}\mathrm{Be}$ solar neutrinos based on a 165.4 kt d exposure of KamLAND. The observed rate is $582\ifmmode\pm\else\textpm\fi{}94$(kt d)${}^{\ensuremath{-}1}$, which corresponds to an 862-keV $^{7}\mathrm{Be}$ solar neutrino flux of $(3.26\ifmmode\pm\else\textpm\fi{}0.52)\ifmmode\times\else\texttimes\fi{}{10}^{9}\phantom{\rule{0.28em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}2}\phantom{\rule{0.16em}{0ex}}{\mathrm{s}}

We present a precision analysis of the ^{136}Xe two-neutrino ββ electron spectrum above 0.8 MeV, based on high-statistics data obtained with the KamLAND-Zen experiment. An improved formalism for the two-neutrino ββ rate allows us to measure the ratio of the leading and subleading 2νββ nuclear matrix elements (NMEs), ξ_{31}^{2ν}=-0.26_{-0.25}^{+0.31}. Theoretical predictions from the nuclear shell model and the majority of the quasiparticle random-phase approximation (QRPA) calculations are consi

Abstract We report on a search for electron antineutrinos ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mover accent="true"> <mml:mrow> <mml:mi>ν</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>¯</mml:mo> </mml:mrow> </mml:mover> </mml:mrow> <mml:mrow> <mml:mi>e</mml:mi> </mml:mrow> </mml:msub> </mml:math> ) from astrophysical sources in the neutrino energy range 8.3–30.8 MeV with the KamLAND detector. In an exposure of 6.72 kton-year of the liq

Abstract We present the results of a search for MeV-scale electron antineutrino events in KamLAND coincident with the 60 gravitational wave events/candidates reported by the LIGO/Virgo collaboration during their second and third observing runs. We find no significant coincident signals within a ±500 s timing window from each gravitational wave and present 90% C.L. upper limits on the electron antineutrino fluence between 10 8 and 10 13 cm −2 for neutrino energies in the energy range of 1.8–111 M

The KamLAND-Zen 800 experiment is searching for the neutrinoless double-beta\ndecay of $^{136}$Xe by using $^{136}$Xe-loaded liquid scintillator. The liquid\nscintillator is enclosed inside a balloon made of thin, transparent,\nlow-radioactivity film that we call Inner Balloon (IB). The IB, apart from\nguaranteeing the liquid containment, also allows to minimize the background\nfrom cosmogenic muon-spallation products and $^{8}$B solar neutrinos. Indeed\nthese events could contribute to the tota

We present a search, using KamLAND, a kiloton-scale anti-neutrino detector, for low-energy anti-neutrino events that were coincident with the gravitational-wave (GW) events GW150914 and GW151226, and the candidate event LVT151012. We find no inverse beta-decay neutrino events within ±500 s of either GW signal. This non-detection is used to constrain the electron anti-neutrino fluence and the total integrated luminosity of the astrophysical sources.