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

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

The recent long-term shutdown of Japanese nuclear reactors has resulted in a significantly reduced reactor νe flux at KamLAND. This running condition provides a unique opportunity to confirm and constrain backgrounds for the reactor νe oscillation analysis. The data set also has improved sensitivity for other νe signals, in particular νe's produced in β-decays from 238 U and 232 Th within the Earth's interior, whose energy spectrum overlaps with that of reactor νe's. Including constraints on θ13 from accelerator and short-baseline reactor neutrino experiments, a combined three-flavor analysis of solar and KamLAND data gives fit values for the oscillation parameters of tan 2 θ12 = 0.436

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 0ν 1/2 > 1.9 × 10 25 yr at 90% C.L. The combined results from KamLAND-Zen and EXO-200 give T 0ν 1/2 > 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. Using those calculations, this result excludes the Majorana neutrino mass range expected from the neutrinoless double-beta decay detection claim in 76 Ge, reported by a part of the Heidelberg-Moscow Collaboration, at more than 97.5% C.L. 21.10.Tg, 14.60.Pq, 27.60.+j Double-beta (ββ) decay is a rare nuclear process observable in even-even nuclei for which ordinary beta decay is energetically forbidden or highly suppressed by large spin differences. Standard ββ decay proceeds by a second-order weak interaction emitting two electron anti neutrinos and two electrons (2νββ). If, however, the neutrino is a massive Majorana particle, ββ decay might also occur without the emission of neutrinos (0νββ). Observation of such a process would demonstrate that lepton number is not conserved in nature. Moreover, if the process is mediated by the exchange of a light left-handed neutrino, its rate increases with the square of the effective Majorana neutrino mass m ββ ≡ Σ i U 2 ei m νi , and hence its measurement would provide information on the absolute neutrino mass scale. To date there has been only one claimed observation of 0νββ decay, in 76 Ge [1].At present there are several operating experiments performing 0νββ decay searches with design sensitivities sufficient to test the Majorana neutrino mass implied by the claim in [1] within a few years of running: GERDA with 76 Ge, CUORE-0 with 130 Te, and EXO-200 and KamLAND-Zen with 136 Xe. Among those experiments, KamLAND-Zen released its first 0νββ half-life limit, T 0ν 1/2 > 5.7 × 10 24 yr at 90% C.L., based on a 27.4 kg yr exposure [2]. Although the sensitivity of this result was impeded by the presence of an unexpected background peak just above the 2.458 MeV Q value of 136 Xe ββ decay, the Majorana neutrino mass sensitivity was similar to that in Ref. [1]. EXO-200 later improved on this limit by a factor of 2.8 [3], constraining the result in [1] for a number of nuclear matrix element (NME) calculations.As shown below, we have found the problematic background peak in the KamLAND-Zen spectrum to most likely come from metastable 110m Ag. We embarked recently on a purification campaign to remove this isotope. Doing so required extracting the Xe from the detector, thus marking the end of the first phase of KamLAND-Zen. In this Letter we report on the full data set from the first phase of KamLAND-Zen, corresponding to an exposure of 89.5 kg yr of 136 Xe. This represents a factor of 3.2 increase over KamLAND-Zen's first result [2], and is also the largest exposure for a ββ decay isot...

A new Super-Kamiokande (SK) search for Supernova Relic Neutrinos (SRNs) was conducted using 2853 live days of data. Sensitivity is now greatly improved compared to the 2003 SK result, which placed a flux limit near many theoretical predictions. This more detailed analysis includes a variety of improvements such as increased efficiency, a lower energy threshold, and an expanded data set. New combined upper limits on SRN flux are between 2.8 and 3.0νe cm −2 s −1 > 16 MeV total positron energy (17.3 MeV Eν).

The results of the third phase of the Super-Kamiokande solar neutrino measurement are presented and compared to the first and second phase results. With improved detector calibrations, a full detector simulation, and improved analysis methods, the systematic uncertainty on the total neutrino flux is estimated to be ±2.1%, which is about two thirds of the systematic uncertainty for the first phase of Super-Kamiokande. The observed 8 B solar flux in the 5.0 to 20 MeV total electron energy region is 2.32± 0.04 (stat.) ± 0.05 (sys.) ×10 6 cm −2 sec −1 under the assumption of pure electron-flavor content, in agreement with previous measurements. A combined oscillation analysis 2 is carried out using SK-I, II, and III data, and the results are also combined with the results of other solar neutrino experiments. The best-fit oscillation parameters are obtained to be sin 2 θ12 = 0.30 by adding KamLAND result. In a three-flavor analysis combining all solar neutrino experiments, the upper limit of sin 2 θ13 is 0.060 at 95% C.L.. After combination with KamLAND results, the upper limit of sin 2 θ13 is found to be 0.059 at 95% C.L..

We present the result of an indirect search for high energy neutrinos from Weakly Interacting Massive Particle (WIMP) annihilation in the Sun using upward-going muon (upmu) events at Super-Kamiokande. Data sets from SKI-SKIII (3109.6 days) were used for the analysis. We looked for an excess of neutrino signal from the Sun as compared with the expected atmospheric neutrino background in three upmu categories: stopping, non-showering, and showering. No significant excess was observed. The 90% C.L. upper limits of upmu flux induced by WIMPs of 100 GeV c -2 were 6.4 × 10 −15 cm −2 s −1 and 4.0 × 10 −15 cm −2 s −1 for the soft and hard annihilation channels, respectively. These limits correspond to upper limits of 4.5 × 10 −39 cm −2 and 2.7 × 10 −40 cm −2 for spin-dependent WIMP-nucleon scattering cross sections in the soft and hard annihilation channels, respectively.

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 2ν 1/2 = 2.38 ± 0.02(stat) ± 0.14(syst) × 10 21 yr, consistent with a recent measurement by EXO-200. We also obtain a lower limit for the neutrinoless double-beta decay half-life, T 0ν 1/2 > 5.7 × 10 24 yr at 90% confidence level (C.L.), which corresponds to almost a five-fold improvement over previous limits.