First Results from KamLAND: Evidence for Reactor Antineutrino Disappearance

KamLAND has measured the flux of {}₄'s from distant nuclear reactors. We find fewer {}₄ events than expected from standard assumptions about {}₄ propagation at the 99. 95% C. L. In a 162 ton exposure the ratio of the observed inverse -decay events to the expected number without {}₄ disappearance is 0. 6110. 085 (stat) 0. 041 (syst) for {}₄ 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.