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This talk reports the latest indications of an anomaly in the measurements of atmospheric neutrinos. New results from Soudan-2 and Super-Kamiokande provide evidence that the ratio of νμ to νe interactions is not as expected. High energy Super-Kamiokande data indicates the cause is a deficit of upward-going νμ, and the zenith angle dependence of the effect is consistent with neutrino oscillations. Upward-going muon measurements by several detectors are discussed, but in total they provide inconclusive evidence for the anomaly.
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E. Kearns (1999) studied this question.