A Neutrino Apparatus with Improved Capabilities for a short baseline $\nu_{\mu}$($\nu_{e}$) <--> $\nu_{\tau}$ search

We propose the conceptual design of a Neutrino ApparatUS with Improved CApAbilities (NAUSICAA). This detector could be used for a new, short-baseline, high sensitivity \osc oscillation search experiment at the CERN-SPS neutrino beam, as well as at the future Fermilab Main Injector neutrino beam. The heart of the detector is a finely instrumented target, made of a sandwich of a light Z material and high resolution tracking detectors. Downstream of the target there are tracking detectors for momentum measurement, followed by a compensating calorimeter. All these systems are contained within magnet providing a magnetic field of about 1 Tesla. Following the magnet there is a muon detector. Unlike previous experiments, NAUSICAA would be capable of searching for the \tau signature using both kinematical and vertex criteria {\it simultaneously}. Detailed Monte Carlo calculations show that NAUSICAA could improve the sensitivity of the on-going experiments, CHORUS and NOMAD by an order of magnitude in a four-year neutrino run at CERN. Further improvement on the sensitivity (by a factor of two to five) could be achieved in a four-year run at Fermilab.