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First Results from KamLAND: Evidence for Reactor Anti-Neutrino Disappearance

KamLAND Collaboration
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Abstract

KamLAND has been used to measure the flux of $\barν_e$'s from distant nuclear reactors. In an exposure of 162 ton$\cdot$yr (145.1 days) the ratio of the number of observed inverse $β$-decay events to the expected number of events without disappearance is $0.611\pm 0.085 {\rm (stat)} \pm 0.041 {\rm (syst)} $ for $\barν_e$ energies $>$ 3.4 MeV. The deficit of events is inconsistent with the expected rate for standard $\barν_e$ propagation at the 99.95% confidence level. In the context of two-flavor neutrino oscillations with CPT invariance, these results exclude all oscillation solutions but the `Large Mixing Angle' solution to the solar neutrino problem using reactor $\barν_e$ sources.

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KamLAND Collaboration. 2002-12-09. First Results from KamLAND: Evidence for Reactor Anti-Neutrino Disappearance. https://doi.org/10.1103/physrevlett.90.021802

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