On the Possible Existence of Heavy Leptons

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Muon–pion invariant mass distributions (Mμπ) observed in neutrino interactions and in the decays of the K0L are compatible with the possible existence of a neutral lepton with a mass in the range 0.422 < Mμπ < 0.437 GeV.

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RAMM, C. On the Possible Existence of Heavy Leptons. Nature 227, 1323–1327 (1970) doi:10.1038/2271323a0

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