  The ideal neutrino detector at the neutrino factory should have a mass in the
range of 10 kton, provide particle identification to tag the flavor of the
incoming neutrino, lepton charge measurement to select the incoming neutrino
helicity, good energy resolution to reconstruct the incoming neutrino energy,
and be isotropic to equally well reconstruct incoming neutrinos from different
baselines (it might be more efficient to build various sources at different
baselines, than various detectors). The detector should also be able to
reconstruct neutrino event typically below 15 GeV. A detector with such quality
is most adapted to fully study neutrino oscillations at the neutrino factory.
In particular, measurement of the leading muons and electrons charge is the
only way to fully simultaneously explore CP and T violation effects. We think
that a magnetized liquid argon imaging detector stands today as the best choice
of technique, that holds the highest promises to match the above mentioned
detector requirements. We discuss also the optimal neutrino factory energy and
baseline between source and detector in order to best perform these studies.
