  This proposal describes an experimental search for sterile neutrinos beyond
the Standard Model with a new CERN-SPS neutrino beam. The experiment is based
on two identical LAr-TPC's followed by magnetized spectrometers, observing the
electron and muon neutrino events at 1600 and 300 m from the proton target.
This project will exploit the ICARUS T600, moved from LNGS to the CERN "Far"
position. An additional 1/4 of the T600 detector will be constructed and
located in the "Near" position. Two spectrometers will be placed downstream of
the two LAr-TPC detectors to greatly complement the physics capabilities.
Spectrometers will exploit a classical dipole magnetic field with iron slabs,
and a new concept air-magnet, to perform charge identification and muon
momentum measurements in a wide energy range over a large transverse area. In
the two positions, the radial and energy spectra of the nu_e beam are
practically identical. Comparing the two detectors, in absence of oscillations,
all cross sections and experimental biases cancel out, and the two
experimentally observed event distributions must be identical. Any difference
of the event distributions at the locations of the two detectors might be
attributed to the possible existence of {\nu}-oscillations, presumably due to
additional neutrinos with a mixing angle sin^2(2theta_new) and a larger mass
difference Delta_m^2_new. The superior quality of the LAr imaging TPC, in
particular its unique electron-pi_zero discrimination allows full rejection of
backgrounds and offers a lossless nu_e detection capability. The determination
of the muon charge with the spectrometers allows the full separation of nu_mu
from anti-nu_mu and therefore controlling systematics from muon
mis-identification largely at high momenta.
