Limits on astrophysical antineutrinos with the KamLAND experiment

TL;DR

This study used the KamLAND detector to search for astrophysical electron antineutrinos in the 8.3 to 30.8 MeV range, setting upper limits on fluxes and constraining models of supernova relic neutrinos and dark matter annihilation.

Contribution

It provides new upper flux limits on astrophysical antineutrinos and constrains models of supernova relic neutrinos and dark matter annihilation using KamLAND data.

Findings

No significant excess of antineutrinos observed over background.

Set upper flux limits of 60–110 cm$^{-2}$ s$^{-1}$ for supernova relic neutrinos.

Improved upper limit on solar $ar{ u}_e$ conversion probability.

Abstract

We report on a search for electron antineutrinos ($\bar{\nu}_e$) from astrophysical sources in the neutrino energy range 8.3 to 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% 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 improves on the upper probability limit of $^{8}$B solar neutrinos converting into $\bar{\nu}_e$'s, $P_{\nu_e \rightarrow \bar{\nu}_e} < 3.5\times10^{-5}$ (90% CL) assuming an undistorted $\bar{\nu}_e$ shape. This corresponds to a solar $\bar{\nu}_e$ flux of 60 cm$^{-2}$ s$^{-1}$ (90% CL) in the analysis energy range.