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) \ifmmode\times\else\texttimes\fi{} U(1) model is constructed and realistic calculations are made of the heavy-lepton production and decay sequence: $\ensuremath{\nu}N\ensuremath{\rightarrow}{M}^{\ensuremath{-}}X$,${M}^{\ensuremath{-}}\ensuremath{\rightarrow}{M}^{0}{l}_{1}^{\ensuremath{-}}\overline{\ensuremath{\nu}}$, ${M}^{0}\ensuremath{\rightarrow}{l}_{2}^{\ensuremath{-}}{l}_{3}^{+}\ensuremath{\nu}$. Good agreement with trimuon data is found, with masses 7 GeV for ${M}^{\ensuremath{-}}$ 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 ${\ensuremath{\mu}}^{\ensuremath{-}}{\ensuremath{\mu}}^{\ensuremath{-}}{\ensuremath{\mu}}^{+}$ and in some ${\ensuremath{\mu}}^{\ensuremath{-}}{\ensuremath{\mu}}^{+}$ 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 ${\ensuremath{\mu}}^{\ensuremath{-}}{\ensuremath{\mu}}^{\ensuremath{-}}$ and ${\ensuremath{\mu}}^{\ensuremath{-}}{\ensuremath{\mu}}^{+}$ events at about five times the ${\ensuremath{\mu}}^{\ensuremath{-}}{\ensuremath{\mu}}^{\ensuremath{-}}{\ensuremath{\mu}}^{+}$ rate. The observed trimuon rate may require a mixing of $\ensuremath{\mu}_{L}^{}{}_{}{}^{\ensuremath{-}}$ with $M_{L}^{}{}_{}{}^{\ensuremath{-}}$ comparable to the Cabibbo angle, which strains conventional universality limits. A generalized mixing scheme which circumvents these limits and allows large ${\ensuremath{\nu}}_{{\ensuremath{\mu}}^{\ensuremath{-}}}{M}^{\ensuremath{-}}$ coupling is presented.