A search for double-beta decays of 136Xe to excited states of 136Ba has been performed with the first phase data set of the KamLAND-Zen experiment. The 01+, 21+ and 22+ transitions of 0νββ decay were ...evaluated in an exposure of 89.5 kg⋅yr of 136Xe, while the same transitions of 2νββ decay were evaluated in an exposure of 61.8 kg⋅yr. No excess over background was found for all decay modes. The lower half-life limits of the 21+ state transitions of 0νββ and 2νββ decay were improved to T1/20ν(0+→21+)>2.6×1025 yr and T1/22ν(0+→21+)>4.6×1023 yr (90% C.L.), respectively. We report on the first experimental lower half-life limits for the transitions to the 01+ state of 136Xe for 0νββ and 2νββ decay. They are T1/20ν(0+→01+)>2.4×1025 yr and T1/22ν(0+→01+)>8.3×1023 yr (90% C.L.). The transitions to the 22+ states are also evaluated for the first time to be T1/20ν(0+→22+)>2.6×1025 yr and T1/22ν(0+→22+)>9.0×1023 yr (90% C.L.). These results are compared to recent theoretical predictions.
A search for double-beta decays of 136Xe to excited states of 136Ba has been performed with the first phase data set of the KamLAND-Zen experiment. The 01+ , 21+ and 22+ transitions of 0νββ decay ...were evaluated in an exposure of 89.5 kg•yr of 136Xe, while the same transitions of 2νββ decay were evaluated in an exposure of 61.8 kg•yr. No excess over background was found for all decay modes. The lower half-life limits of the 21+ state transitions of 0νββ and 2νββ decay were improved to T$0v\atop{1/2}$(0+ →21+) > 2.6×1025 yr and T$2v\atop{1/2}$ (0+ →21+) > 4.6×1023 yr (90% C.L.), respectively. We report on the first experimental lower half-life limits for the transitions to the 01+ state of 136Xe for 0νββ and 2νββ decay. They are T$0v\atop{1/2}$(0+ →01+) > 2.4×1025 yr and T$2v\atop{1/2}$(0+ →01+) > 8.3×1023 yr (90% C.L.). The transitions to the 22+ states are also evaluated for the first time to be T$0v\atop{1/2}$(0+ →22+) > 2.6×1025 yr and T$2v\atop{1/2}$(0+ →22+) > 9.0×1023 yr (90% C.L.). Finally, these results are compared to recent theoretical predictions.
We report a measurement of the neutrino-electron elastic scattering rate of 862 keV 7Be solar neutrinos based on a 165.4 kt d exposure of KamLAND. The observed rate is 582±94(kt d)₋1, which ...corresponds to an 862-keV 7Be solar neutrino flux of (3.26±0.52)×109cm₋2s₋1, assuming a pure electron-flavor flux. Comparing this flux with the standard solar model prediction and further assuming three-flavor mixing, a νe survival probability of 0.66±0.15 is determined from the KamLAND data. Lastly, utilizing a global three-flavor oscillation analysis, we obtain a total 7Be solar neutrino flux of (5.82±1.02)×109cm₋2s₋1, which is consistent with the standard solar model predictions.
The Kamioka Liquid scintillator Anti-Neutrino Detector is used in a search for single neutron or two-neutron intranuclear disappearance that would produce holes in the -shell energy level of (12)C ...nuclei. Such holes could be created as a result of nucleon decay into invisible modes (inv), e.g., n--> 3v or nn--> 2v. The deexcitation of the corresponding daughter nucleus results in a sequence of space and time-correlated events observable in the liquid scintillator detector. We report on new limits for one- and two-neutron disappearance: tau(n--> inv) > 5.8 x 10(29) years and tau (nn--> inv) > 1.4 x 10(30) years at 90% C.L. These results represent an improvement of factors of approximately 3 and >10(4) and over previous experiments.
We describe a compact, ultra-clean device used to deploy radioactive sources along the vertical axis of the KamLAND liquid-scintillator neutrino detector for purposes of calibration. The device ...worked by paying out and reeling in precise lengths of a hanging, small-gauge wire rope (cable); an assortment of interchangeable radioactive sources could be attached to a weight at the end of the cable. All components exposed to the radiopure liquid scintillator were made of chemically compatible UHV-cleaned materials, primarily stainless steel, in order to avoid contaminating or degrading the scintillator. To prevent radon intrusion, the apparatus was enclosed in a hermetically sealed housing inside a glove box, and both volumes were regularly flushed with purified nitrogen gas. Finally, an infrared camera attached to the side of the housing permitted real-time visual monitoring of the cable’s motion, and the system was controlled via a graphical user interface.
(ProQuest: ... denotes formulae and/or non-USASCII text omitted) The recent long-term shutdown of Japanese nuclear reactors has resulted in a significantly reduced reactor nu sub(e) flux at KamLAND. ...This running condition provides a unique opportunity to confirm and constrain backgrounds for the reactor nu sub(e) oscillation analysis. The data set also has improved sensitivity for other nu sub(e) signals, in particular nu sub(e)'s produced in beta -decays from super(238)U and super(232)Th within the Earth's interior, whose energy spectrum overlaps with that of reactor nu sub(e)'s. Including constraints on theta sub(13) 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 super(2)theta sub(12) = ..., ... = ..., and sin super(2)theta sub(13) = ... Assuming a chondritic Th/U mass ratio, we obtain ... nu sub(e) events from super(238)U and super(232)Th, corresponding to a geo nu sub(e) flux of ... x 10 super(6) cm super(-2) s super(-1) at the KamLAND location. We evaluate various bulk silicate Earth composition models using the observed geo nu sub(e) rate.
The removal of radioactivity from liquid scintillator has been studied in preparation of a low background phase of KamLAND. This paper describes the methods and techniques developed to measure and ...efficiently extract radon decay products from liquid scintillator. We report the radio-isotope reduction factors obtained when applying various extraction methods. During this study, distillation was identified as the most efficient method for removing radon-born lead from liquid scintillator.
The removal of radioactivity from liquid scintillator has been studied in preparation of a low background phase of KamLAND. This paper describes the methods and techniques developed to measure and ...efficiently extract radon decay products from liquid scintillator. We report the radio isotope reduction factors obtained when applying various extraction methods. During this study, distillation was identified as the most efficient method for removing radon-born lead from liquid scintillator.
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