Neutrino oscillation physics with a neutrino factory

Data from atmospheric and solar neutrinos indicate that there are at least three neu-trino types involved in oscillation phenomena. Even if the corresponding neutrino mass scales are very dierent, the inevitable reference to mixing between more than two neutrino types has profound consequences on the planning of the accelerator ex-periments suggested by these results. We discuss the measurement of mixing angles and CP phases in the context of the neutrino beam emanating from a neutrino factory: the straight sections of a muon storage ring. We emphasize the importance of charge identi cation. The appearance of wrong sign muons in a long baseline experiment may provide a powerful test of neutrino oscillations in the mass-dierence range indicated by atmospheric-neutrino observations.