Extending sensitivity for low-mass neutral heavy lepton searches

We point out the importance of two-body final states of weak isosinglet neutral heavy leptons predicted in several models of new physics beyond the standard model. We concentrate on muon-type neutral heavy leptons $L_{\mu }^0$ with a mass $M<\mathrm{}2\mathrm{}$ GeV that can be searched for with increased sensitivity at a new round of neutrino experiments at CERN and Fermilab. Providing explicit decay rate formulas for the $\mathrm{ee}\nu$, $e\mu \nu$, $\mu \mu \nu$, $\pi \mu$, $\rho \mu$, and $a_1\mu$ final states, we use general scaling features to estimate the sensitivity of $L_{\mu }^0$ searches in current and future experiments, emphasizing the importance of the $\pi \mu$ decay mode.