Mu + N --> Tau + N at a Muon or Neutrino Factory

The experimental discovery of large nu_mu-nu_tau mixing indicates that analogous mixing in the charged lepton sector could be substantial. We consider the possibility that if a high intensity muon beam, perhaps at the early stages of a muon or neutrino factory, strikes a nuclear target, then conversion of some of the muons into tau leptons could occur (similar to the conversion of muons to electrons at MECO). Using current experimental limits on rare tau decays to bound the size of the relevant operators, we find that a 50 GeV muon beam, with 10^20 muons on target per year, could yield as many as 10^7 mu + N --> tau + N events per year. Backgrounds could be substantial, and we comment on the possibility of detection of this process.