Cascade decays of heavy leptons produced by neutrinos

Gauge models with two heavy leptons that decay sequentially are proposed as a mechanism for fast multilepton production by neutrinos. To quantify the predictions of such models, a specific SU(2) ×{} U(1) model is constructed and realistic calculations are made of the heavy-lepton production and decay sequence: νN→M^-X,M^-→M⁰l₁^-ν, M⁰→l₂^-l₃⁺ν. Good agreement with trimuon data is found, with masses 7 GeV for M^- and 2-4 GeV for M⁰. The information contained in experimental distributions of multilepton events is explored. Azimuth-momentum correlations exclude a hadron-vertex origin for the extra muons in μ^-μ^-μ⁺ and in some μ^-μ⁺ events. The two undetected decay neutrinos carry off missing energy equal to 35% of the visible energy on the average; this prediction can be tested with narrow-band beams. The cascade mechanism gives rise to μ^-μ^- and μ^-μ⁺ events at about five times the μ^-μ^-μ⁺ rate. The observed trimuon rate may require a mixing of μL^_^- with ML^_^- comparable to the Cabibbo angle, which strains conventional universality limits. A generalized mixing scheme which circumvents these limits and allows large ν_μ^-M^- coupling is presented.