First direct observation of Muon antineutrino disappearance

Abstract

This Letter reports the first direct observation of muon antineutrino disappearance. The MINOS experiment has taken data with an accelerator beam optimized for ν̄μ production, accumulating an exposure of 1.71×1020 protons on target. In the Far Detector, 97 charged current ν̄μ events are observed. The no-oscillation hypothesis predicts 156 events and is excluded at 6.3σ. The best fit to oscillation yields |Δm⊃̄2|=[3.36-0.40+0.46(stat)±0.06(syst)] ×10⊃-3eV2, ⊃sin⊃2(2θ̄)=0.86-0.12+0.11(stat) ±0.01(syst). The MINOS νμ and ν̄μ measurements are consistent at the 2.0% confidence level, assuming identical underlying oscillation parameters. © 2011 American Physical Society

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