We present an improved search for neutrinoless double-beta (0νββ) decay of 136 Xe in the KamLANDZen 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 0ν 1=2 > 1.07 × 10 26 yr at 90% C.L., an almost sixfold improvement over previous limits. Using commonly adopted nuclear matrix element calculations, the corresponding upper limits on the effective Majorana neutrino mass are in the range 61-165 meV. For the most optimistic nuclear matrix elements, this limit reaches the bottom of the quasidegenerate neutrino mass region. DOI: 10.1103/PhysRevLett.117.082503 Neutrinoless double-beta (0νββ) decay is an exotic nuclear process predicted by extensions of the Standard Model of particle physics. Observation of this decay demonstrates the nonconservation of lepton number, and proves that neutrinos have a Majorana mass component. In the framework of light Majorana neutrino exchange, its decay rate is proportional to the square of the effective Majorana neutrino mass hm ββ i ≡ j P i U 2 ei m ν i j. ) provide upper limits on hm ββ i of ∼0.2-0.4 eV using available nuclear matrix element (NME) values from the literature. The sensitivities of these searches correspond to mass scales in the so-called quasidegenerate mass region.KamLAND-Zen is a double-beta decay experiment that exploits the existing detection infrastructure and radiopurity of KamLAND [5,6]. The KamLAND-Zen detector consists of 13 tons of Xe-loaded liquid scintillator (Xe-LS) contained in a 3.08-m-diameter spherical inner balloon (IB) located at the center of the KamLAND detector. The IB is constructed from 25-μm-thick transparent nylon film and is surrounded by 1 kton of liquid scintillator (LS) contained in a 13-m-diameter spherical outer balloon. The outer LS acts as an active shield. The scintillation photons are viewed by 1879 photomultiplier tubes (PMTs) mounted on the inner surface of the containment vessel. The Xe-LS consists of 80.7% decane and 19.3% pseudocumene (1,2,4-trimethylbenzene) by volume, 2.29 g=liter of the fluor PPO (2,5-diphenyloxazole), and ð2.91 AE 0.04Þ% by weight of isotopically enriched xenon gas. The isotopic abundances in the enriched xenon were measured by a residual gas analyzer to be ð90.77 AE 0.08Þ% 136 Xe, ð8.96AE 0.02Þ% 134 Xe. Other xenon isotopes have negligible presence. The two electrons emitted from 136 Xe ββ decay

Solar neutrino measurements from 1258 days of data from the Super-Kamiokande detector are presented [? ]. The measurements are based on recoil electrons in the energy range 5.0-20.0 MeV. The measured solar neutrino flux is 2.32 ± 0.03 (stat.) +0.08 −0.07 (sys.) ×10 6 cm −2 s −1 , which is 45.1 ± 0.5 (stat.) +1.6 −1.4 (sys.)% of that predicted by the BP2000 SSM. The day vs night flux asymmetry (Φn − Φ d )/Φaverage is 0.033 ± 0.022 (stat.) +0.013 −0.012 (sys.). The recoil electron energy spectrum is consistent with no spectral distortion (χ 2 /d.o.f. = 19.0/18). The seasonal variation of the flux is consistent with that expected from the eccentricity of the Earth's orbit (χ 2 /d.o.f. = 3.7/7). For the hep neutrino flux, we set a 90% C.L. upper limit of 40 × 10 3 cm −2 s −1 , which is 4.3 times the BP2000 SSM prediction.22 This preprint is almost identical to the report submitted to Physical Review Letter. We have added to this preprint a few tables of

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