The neutrino oscillation probabilities at the long-baseline accelerator neutrino experiments are expected to be modified by matter effects. We search for evidence of such modification in the data of T2K and NOνA, by fitting the data to the hypothesis of (a) matter modified oscillations and (b) vacuum oscillations. We find that vacuum oscillations provide as good a fit to the data as matter modified oscillations. Even extended runs of T2K and NOνA, with five years in neutrino mode (5ν) and five years in anti-neutrino mode (5ν̄), cannot make a 3σ distinction between vacuum and matter modified oscillations. The future experiment DUNE, with neutrino and anti-neutrino runs of five years each (5ν + 5ν̄), can rule out vacuum oscillations by itself at 5σ if the hierarchy is normal. If the hierarchy is inverted, a 5σ discrimination against vacuum oscillations requires the combination of (5ν + 5ν̄) runs of T2K, NOνA and DUNE.

中文翻译：

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长基线加速器中微子实验中的物质与真空振荡

长基线加速器中微子实验中的中微子振荡概率预计会受到物质效应的影响。我们在 T2K 和 NO 的数据中寻找这种修改的证据νA，通过将数据拟合到（a）物质修正振荡和（b）真空振荡的假设。我们发现真空振荡提供了与物质修正振荡一样好的数据拟合。甚至延长 T2K 和 NOνA，中微子模式五年(5ν)和五年的反中微子模式(5ν̄), 不能做3σ真空和物质修正振荡之间的区别。未来的实验 DUNE，中微子和反中微子各运行五年(5ν + 5ν̄), 可以自行排除真空振荡5σ如果层次结构正常。如果层次结构倒置，则5σ对真空振荡的歧视需要结合(5ν + 5ν̄)T2K 运行，否ν一个和沙丘。