Cascade decays of heavy leptons produced by neutrinos

Abstract

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: $\nu N\to M^{-}X$,$M^{-}\to M^0{l}_1^{-}\overline{\nu }$, $M^0\to l_2^{-}{l}_3^{+}\nu$. Good agreement with trimuon data is found, with masses 7 GeV for $M^{-}$ and 2-4 GeV for $M^0$. The information contained in experimental distributions of multilepton events is explored. Azimuth-momentum correlations exclude a hadron-vertex origin for the extra muons in ${\mu }^{-}{\mu }^{-}{\mu }^{+}$ and in some ${\mu }^{-}{\mu }^{+}$ 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 ${\mu }^{-}{\mu }^{-}$ and ${\mu }^{-}{\mu }^{+}$ events at about five times the ${\mu }^{-}{\mu }^{-}{\mu }^{+}$ rate. The observed trimuon rate may require a mixing of $\mu _L^{}{}_{}{}^{-}$ with $M_L^{}{}_{}{}^{-}$ comparable to the Cabibbo angle, which strains conventional universality limits. A generalized mixing scheme which circumvents these limits and allows large ${\nu }_{{\mu }^{-}}{M}^{-}$ coupling is presented.