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School of Chemistry and Physics, University of Adelaide, Adelaide, South Australia 5005, Australia.
DESY, D-15735 Zeuthen, Germany.
Phys Rev Lett. 2015 May 1;114(17):171102. doi: 10.1103/PhysRevLett.114.171102. Epub 2015 Apr 28.
A diffuse flux of astrophysical neutrinos above 100 TeV has been observed at the IceCube Neutrino Observatory. Here we extend this analysis to probe the astrophysical flux down to 35 TeV and analyze its flavor composition by classifying events as showers or tracks. Taking advantage of lower atmospheric backgrounds for showerlike events, we obtain a shower-biased sample containing 129 showers and 8 tracks collected in three years from 2010 to 2013. We demonstrate consistency with the (fe:fμ:fτ)⊕≈(1:1:1)⊕ flavor ratio at Earth commonly expected from the averaged oscillations of neutrinos produced by pion decay in distant astrophysical sources. Limits are placed on nonstandard flavor compositions that cannot be produced by averaged neutrino oscillations but could arise in exotic physics scenarios. A maximally tracklike composition of (0:1:0)⊕ is excluded at 3.3σ, and a purely showerlike composition of (1:0:0)⊕ is excluded at 2.3σ.
在冰立方中微子天文台观测到了能量高于100 TeV的天体物理中微子的漫射通量。在此，我们将此分析扩展到探测低至35 TeV的天体物理通量，并通过将事件分类为簇射或径迹来分析其味成分。利用类簇射事件较低的大气本底，我们获得了一个偏向簇射的样本，其中包含2010年至2013年三年间收集的129个簇射和8个径迹。我们证明了与地球处通常预期的（fe:fμ:fτ）⊕≈(1:1:1)⊕味比一致，这是由遥远天体物理源中π介子衰变产生的中微子平均振荡所导致的。对无法由中微子平均振荡产生但可能出现在奇异物理情景中的非标准味成分设置了限制。最大径迹类成分（0:1:0）⊕在3.3σ水平被排除，而纯簇射类成分（1:0:0）⊕在2.3σ水平被排除。
