Are Heavy Leptons Found?

Recently reported observations suggest the existence of a new particle without strong interactions. We interpret it as a massive neutral lepton $L^0$ produced by decays of a new charged lepton $L^{\pm }$ which in turn is pair-produced electromagnetically by cosmic rays. The mass of $L^{\pm }$ must be ∼2 GeV; the lifetime of $L^0$ must be ∼ ${10}^{-5\mathrm{}}$ sec. Possible gauge models incorporating the new leptons are discussed, as are other experimental consequences.