First Results from KamLAND: Evidence for Reactor Antineutrino Disappearance
KamLAND has measured the flux of v̅ₑ’s from distant nuclear reactors. We find fewer v̅ₑ events than expected from standard assumptions about v̅ₑ propagation at the 99.95% C.L. In a 162 ton ∙ yr exposure the ratio of the observed inverse β-decay events to the expected number without v̅ₑ disappearance is 0.611 ± 0.085(stat) ± 0.041(syst) for v̅ₑ 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.