Abstract
Abstract We report on a search for electron antineutrinos ( ν ¯ e ) from astrophysical sources in the neutrino energy range 8.3–30.8 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 60–110 cm−2 s−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 ¯ e , P ν e → ν ¯ e < 3.5 × 10 − 5 (90% CL) assuming an undistorted ν ¯ e shape. This corresponds to a solar ν ¯ e flux of 60 cm−2 s−1 (90% CL) in the analysis energy range.
Highlights
Underground liquid-scintillator neutrino detectors observe geo neutrinos, solar neutrinos, and reactor neutrinos below 10 MeV energy, in addition to the atmospheric neutrinos peak at O(GeV) range
We present a search for astrophysical neutrinos in the neutrino energy between 8.3 and 30.8 MeV, focusing on electron antineutrinos from the Sun, past supernovae, and dark matter annihilation
The fast neutron background contributes with a large uncertainty but is mostly concentrated at the outer radius, while the other backgrounds and neutrino candidates have a uniform distribution in the detector
Summary
Underground liquid-scintillator neutrino detectors observe geo neutrinos, solar neutrinos, and reactor neutrinos below 10 MeV energy, in addition to the atmospheric neutrinos peak at O(GeV) range. Other astrophysical neutrino sources exist in our universe: from supernova explosions to hypothetical dark-matter annihilation neutrinos. We present a search for astrophysical neutrinos in the neutrino energy between 8.3 and 30.8 MeV, focusing on electron antineutrinos (νe) from the Sun, past supernovae, and dark matter annihilation. In case of the existence of an MeV-scale light dark matter particle, its self-annihilation process might produce neutrino pairs (χχ → νν) at MeV energies.
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