We present the results of a search for extraterrestrial electron antineutrinos ( 's) in the energy range 8.3 MeV < Eve < 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 ν e 's converting into Ve 's at 5.3 × 10-5 (90% CL), if we assume an undistorted Ve shape. This limit corresponds to a solar Ve flux of 93 cm-2 s-1 or an event rate of 1.6 events (kton - year)-1 above the energy threshold (Eve ≥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
