Abstract
In January 22, 2002, KamLAND started the data-taking. With the data sample from March 3 through October 6, 2002. KamLAND has measured the flux of electron antineutrinos from distant nuclear reactors. We find fewer electron antineutrino events than expected from standard assumptions about electron antineutrino propagation at the 99.95%C.L. In a 162 ton-yr exposure the ratio of the number of observed inverse β-decay events to the expected number without electron antineutrino disappearance is 0.611±0.085 (stat) ± 0.041 (syst) for electron antineutrino energies >3.4 MeV. In the context of two-flavor neutrino oscillations with CPT invariance, all solutions to the solar neutrino problem except for the "large mixing angle" region are excluded.
