Majorana vs. Dirac sterile neutrinos lighter than M_W at the LHC

We propose to study the leptonic decays W^± → e^±e^±μ ^∓ ν and W^± → μ^±μ^±e ^∓ ν at the LHC to discover sterile neutrinos with masses below M_W , and discriminate their Majorana or Dirac character. These decays are induced by a sterile neutrino N that goes on mass shell in the intermediate state. We find that, even though the final (anti-)neutrino goes undetected and thus lepton number is unchecked, one can distinguish between the Majorana vs. Dirac character of the intermediate sterile neutrino by comparing the production of e^±e^±μ ^∓ vs. μ^±μ^±e ^∓, provided the N-e and N-μ mixings are different enough. Alternatively, one can also distinguish the Majorana vs. Dirac character by studying the energy spectra of the opposite charge lepton, a method that works even if the N-e and N-μ mixings are equal.