Search

We report on a search for electron antineutrinos ( ν ÂŻ e ) from astrophysical sources in the neutrino energy range 8.3â€"30.8 MeV with the KamLAND detector. In an exposure of 6.72 kton-year of the liquid scintillator, we observe 18 candidate events via the inverse beta decay reaction. Although there is a large background uncertainty from neutral current atmospheric neutrino interactions, we find no significant excess over background model predictions. Assuming several supernova relic neutrino spectra, we give upper flux limits of 60â€"110 cmâˆ'2 sâˆ'1 (90% confidence level, CL) in the analysis range and present a model-independent flux. We also set limits on the annihilation rates for light dark matter pairs to neutrino pairs. These data improve on the upper probability limit of 8B solar neutrinos converting into ν ÂŻ e , P ν e â†' ν ÂŻ e < 3.5 Ă— 10 âˆ' 5 (90% CL) assuming an undistorted ν ÂŻ e shape. This corresponds to a solar ν ÂŻ e flux of 60 cmâˆ'2 sâˆ'1 (90% CL) in the analysis energy range. [ABSTRACT FROM AUTHOR]

The detection of electron antineutrinos produced by natural radioactivity in the Earth could yield important geophysical information. The Kamioka liquid scintillator antineutrino detector (KamLAND) has the sensitivity to detect electron antineutrinos produced by the decay of 238U and 232Th within the Earth. Earth composition models suggest that the radiogenic power from these isotope decays is 16 TW, approximately half of the total measured heat dissipation rate from the Earth. Here we present results from a search for geoneutrinos with KamLAND. Assuming a Th/U mass concentration ratio of 3.9, the 90 per cent confidence interval for the total number of geoneutrinos detected is 4.5 to 54.2. This result is consistent with the central value of 19 predicted by geophysical models. Although our present data have limited statistical power, they nevertheless provide by direct means an upper limit (60 TW) for the radiogenic power of U and Th in the Earth, a quantity that is currently poorly constrained. [ABSTRACT FROM AUTHOR]

Particle dark matter could belong to a multiplet that includes an electrically charged state. WIMP dark matter (χ 0) accompanied by a negatively charged excited state (χ −) with a small mass difference (e.g. < 20 MeV) can form a bound-state with a nucleus such as xenon. This bound-state formation is rare and the released energy is O (1 − 10) MeV depending on the nucleus, making large liquid scintillator detectors suitable for detection. We searched for bound-state formation events with xenon in two experimental phases of the KamLAND-Zen experiment, a xenon-doped liquid scintillator detector. No statistically significant events were observed. For a benchmark parameter set of WIMP mass m χ 0 = 1 TeV and mass difference Δ m = 17 MeV, we set the most stringent upper limits on the recombination cross section times velocity 〈 σ v 〉 and the decay-width of χ − to 9.2 × 10 − 30 c m 3 / s and 8.7 × 10 − 14 GeV, respectively at 90% confidence level. [ABSTRACT FROM AUTHOR]

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. 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. [ABSTRACT FROM AUTHOR]