High Sensitivity Anti-Neutrino Detection by KamLAND

Abstract

Electron anti-neutrinos from nuclear power reactors have been observed by KamLAND. Data from 0.16 kton-year exposure (145.1 live days) indicates disappearance of electron anti-neutrinos at 99.95% C.L. in the energy range 2.6 MeV < E < 8.0 MeV. Considering two-flavor neutrino oscillation with CPT invariance, the only remaining solution to the solar neutrino problem is the Large Mixing Angle (LMA) solution. In addition a 0.28kton-year exposure (185.5 live days) was searched for electron anti-neutrinos in the energy range 8.3 MeV < E < 14.8 MeV. No candidate events were found with expected background of 1.1 +- 0.4 events. Assuming that the origin of electron anti-neutrinos in this energy region comes from 8B solar electron neutrinos, we find an upper limit of neutrino to anti-neutrino conversion probability of 0.00028.