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]

We report the result of a search for neutrinos in coincidence with solar flares from the GOES flare database. The search was performed on a 10.8 kton-year exposure of KamLAND collected from 2002 to 2019. This large exposure allows us to explore previously unconstrained parameter space for solar flare neutrinos. We found no statistical excess of neutrinos and established 90% confidence level upper limits of 8.4 × 107 cm−2 (3.0 × 109 cm−2) on the electron antineutrino (electron neutrino) fluence at 20 MeV normalized to the X12 flare, assuming that the neutrino fluence is proportional to the X-ray intensity. [ABSTRACT FROM AUTHOR]

We present the results of a search for extraterrestrial electron antineutrinos (퐯̄e's) in the energy range 8.3 MeV < E퐯̄e < 31.8 MeV using the KamLAND detector. In an exposure of 4.53 kton-year, we identify 25 candidate events. All of the candidate events can be attributed to background, most importantly neutral current atmospheric neutrino interactions, setting an upper limit on the probability of 8B solar ve's converting into 퐯̄e's at 5.3 x 10-5 (90% CL), if we assume an undistorted 퐯̄e shape. This limit corresponds to a solar 퐯̄e flux of 93 cm-2 s-1 or an event rate of 1.6 events (kton-year)-1 above the energy threshold (E퐯̄e ≳ 8.3 MeV). The present data also allows us to set more stringent limits on the diffuse supernova neutrino flux and on the annihilation rates for light dark matter particles. [ABSTRACT FROM AUTHOR]