LAUSR

We reanalyze the results of the searches for Heavy Neutral Leptons (HNLs) by the CHARM experiment. We study HNL decay channel N → e þ e − ν = μ þ μ − ν and show that, in addition to the constraints on the HNL ’ s mixings with ν e or ν μ , the same data also implies limits on the HNLs that mix only with ν τ and have masses in the range 290 MeV < m N ≲ 1 . 6 GeV: the region in the parameter space that was considered in the literature as a target for HNLs searches.