Search for extraterrestrial antineutrino sources with the KamLAND detector

TL;DR

This study used the KamLAND detector to search for extraterrestrial electron antineutrinos in the 8.3 to 31.8 MeV range, finding no excess events and setting upper limits on their flux, as well as on related astrophysical and dark matter phenomena.

Contribution

First search for extraterrestrial electron antineutrinos in this energy range using KamLAND, establishing new upper limits and constraining models of solar, supernova, and dark matter sources.

Findings

No excess antineutrino events detected beyond background expectations.

Set an upper limit on solar antineutrino flux at 93 cm^{-2} s^{-1}.

Provided more stringent limits on diffuse supernova neutrino flux and dark matter annihilation rates.

Abstract

We present the results of a search for extraterrestrial electron antineutrinos ($\bar{\nu}_{e}$'s) in the energy range $8.3 MeV < E_{\bar{\nu}_{e}} < 31.8 MeV$ 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 $^{8}$B solar $\nu_{e}$'s converting into $\bar{\nu}_{e}$'s at $5.3 \times 10^{-5}$ (90% C.L.), if we assume an undistorted $\bar{\nu}_{e}$ shape. This limit corresponds to a solar $\bar{\nu}_{e}$ flux of $93 cm^{-2} s^{-1}$ or an event rate of $1.6 events (kton-year)^{-1}$ above the energy threshold $(E_{\bar{\nu}_{e}} > 8.3 MeV)$. 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.