We present the results of a search for extraterrestrial electron antineutrinos ( \overline { \nu } _ { e } ’ s ) in the energy range 8.3 { MeV } < E _ { \overline { \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 \overline { \nu } _ { e } ’ s at 5.3 \times 10 ^ { -5 } ( 90 % CL ) , if we assume an undistorted \overline { \nu } _ { e } shape .
This limit corresponds to a solar \overline { \nu } _ { e } flux of 93 { cm ^ { -2 } s ^ { -1 } } or an event rate of 1.6 { events ( kton \mathchar 45 year ) ^ { -1 } } above the energy threshold ( E _ { \overline { \nu } _ { e } } \geq 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 .