Study of atmospheric neutrinos

大气中的中微子来自于π介子（和K介子）的衰变，而π介子（和K介子）是由大气中的初级宇宙射线相互作用产生的。预计μ中微子和电子中微子之间的通量比约为2。然而，Kamiokande关于该比率的实验结果约为1.2。在本研究计划中，我们进行了详细的通量计算、大气中微子样品中的中子本底研究和高能大气μ子中微子产生的上行μ子分析。我们发现类电子样品的中子本底污染小于1%。对上行μ子的分析表明，如果考虑中微子振荡效应，上行μ子数据与完全包含的大气中微子事件是一致的。从这些研究中，我们得出结论，目前的数据可能是中微子振荡的证据。numu*nue和numu*nutau振荡通道都可以解释目前的数据。

Atmospheric neutrinos arise from the decay of pions (and kaons) produced by primary cosmic-ray interactions in the atmosphere. It is expected that the flux ratio between muon neutrinos and electron neutrinos is about 2. However, the experimental result from Kamiokande on this ratio was about 1.2. This observation, if confirmed, could be evidence for neutrino oscillations and is potentially very important.In this research project, we carried out a detailed flux calculation, a study of neutron background in the atmospheric neutrino sample and an analysis of upward-going muons which were produced by high energy atmospheric muon neutrinos. We found that the contamination of neutron background in the electron-like sample was less than 1%. The analysis of the upward-going muons suggested that the upward-going muon data were consistent with the fully contained atmospheric neutrino events if the neutrino oscillation effects were taken into account. From these studies, we concluded that the present data could be evidence for neutrino oscillations. Both the numu*nue and numu*nutau oscillation channels could explain the present data.