In this work, we report the results of a search for MeV-scale astrophysical neutrinos in KamLAND presented as an excess in the number of coincident neutrino interactions associated with the publicly ...available high-energy neutrino datasets from the IceCube Neutrino Observatory. We find no statistically significant excess in the number of observed low-energy electron antineutrinos in KamLAND, given a coincidence time window of ±500 s, ±1,000 s, ±3,600 s, and ±10,000 s around each of the IceCube neutrinos. We use this observation to present limits from 1.8 MeV to 100 MeV on the electron antineutrino fluence, assuming a mono-energetic flux. We then compare the results to several astrophysical measurements performed by IceCube and place a limit at the 90% confidence level on the electron antineutrino isotropic thermal luminosity from the TXS 0506+056 blazar.
The KamLAND-Zen experiment has provided stringent constraints on the neutrinoless double-beta (\(0\nu\beta\beta\)) decay half-life in \(^{136}\)Xe using a xenon-loaded liquid scintillator. We report ...an improved search using an upgraded detector with almost double the amount of xenon and an ultralow radioactivity container, corresponding to an exposure of 970 kg yr of \(^{136}\)Xe. These new data provide valuable insight into backgrounds, especially from cosmic muon spallation of xenon, and have required the use of novel background rejection techniques. We obtain a lower limit for the \(0\nu\beta\beta\) decay half-life of \(T_{1/2}^{0\nu} > 2.3 \times 10^{26}\) yr at 90% C.L., corresponding to upper limits on the effective Majorana neutrino mass of 36-156 meV using commonly adopted nuclear matrix element calculations.
Cosmic-ray muons produce various radioisotopes when passing through material. These spallation products can be backgrounds for rare event searches such as in solar neutrino, double-beta decay, and ...dark matter search experiments. The KamLAND-Zen experiment searches for neutrinoless double-beta decay in 745kg of xenon dissolved in liquid scintillator. The experiment includes dead-time-free electronics with a high efficiency for detecting muon-induced neutrons. The production yields of different radioisotopes are measured with a combination of delayed coincidence techniques, newly developed muon reconstruction and xenon spallation identification methods. The observed xenon spallation products are consistent with results from the FLUKA and Geant4 simulation codes.
The decay of the primordial isotopes \(^{238}\mathrm{U}\), \(^{235}\mathrm{U}\), \(^{232}\mathrm{Th}\), and \(^{40}\mathrm{K}\) have contributed to the terrestrial heat budget throughout the Earth's ...history. Hence the individual abundance of those isotopes are key parameters in reconstructing contemporary Earth model. The geoneutrinos produced by the radioactive decays of uranium and thorium have been observed with the Kamioka Liquid-Scintillator Antineutrino Detector (KamLAND). Those measurements have been improved with more than 18-year observation time, and improvements in detector background levels mainly by an 8-year almost rector-free period now permit spectroscopy with geoneutrinos. Our results yield the first constraint on both uranium and thorium heat contributions. Herein the KamLAND result is consistent with geochemical estimations based on elemental abundances of chondritic meteorites and mantle peridotites. The High-Q model is disfavored at 99.76% C.L. and a fully radiogenic model is excluded at 5.2\(\sigma\) assuming a homogeneous heat producing element distribution in the mantle.
We present the results of a search for core-collapse supernova neutrinos, using long-term KamLAND data from 2002 March 9 to 2020 April 25. We focus on the electron antineutrinos emitted from ...supernovae in the energy range of 1.8--111 MeV. Supernovae will make a neutrino event cluster with the duration of \(\sim\)10 s in the KamLAND data. We find no neutrino clusters and give the upper limit on the supernova rate as to be 0.15 yr\(^{-1}\) with a 90% confidence level. The detectable range, which corresponds to a >95% detection probability, is 40--59 kpc and 65--81 kpc for core-collapse supernovae and failed core-collapse supernovae, respectively. This paper proposes to convert the supernova rate obtained by the neutrino observation to the Galactic star formation rate. Assuming a modified Salpeter-type initial mass function, the upper limit on the Galactic star formation rate is <(17.5--22.7) \(M_{\odot} \mathrm{yr}^{-1}\) with a 90% confidence level.
We report the results of a search for MeV-scale astrophysical neutrinos in KamLAND presented as an excess in the number of coincident neutrino interactions associated with the publicly available ...high-energy neutrino datasets from the IceCube Neutrino Observatory. We find no statistically significant excess in the number of observed low-energy electron antineutrinos in KamLAND, given a coincidence time window of \(\pm\)500s, \(\pm\)1,000s, \(\pm\)3,600s, and \(\pm\)10,000s around each of the IceCube neutrinos. We use this observation to present limits from 1.8 MeV to 100 MeV on the electron antineutrino fluence, assuming a mono-energetic flux. We then compare the results to several astrophysical measurements performed by IceCube and place a limit at the 90% confidence level on the electron antineutrino isotropic thermal luminosity from the TXS 0506+056 blazar.
The origins of high-energy astrophysical neutrinos remain a mystery despite extensive searches for their sources. We present constraints from seven years of IceCube Neutrino Observatory muon data on ...the neutrino flux coming from the Galactic plane. This flux is expected from cosmic-ray interactions with the interstellar medium or near localized sources. Two methods were developed to test for a spatially extended flux from the entire plane, both of which are maximum likelihood fits but with different signal and background modeling techniques. We consider three templates for Galactic neutrino emission based primarily on gamma-ray observations and models that cover a wide range of possibilities. Based on these templates and in the benchmark case of an unbroken E{sup −2.5} power-law energy spectrum, we set 90% confidence level upper limits, constraining the possible Galactic contribution to the diffuse neutrino flux to be relatively small, less than 14% of the flux reported in Aartsen et al. above 1 TeV. A stacking method is also used to test catalogs of known high-energy Galactic gamma-ray sources.
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