  We present a study for a design of a long baseline nu_mu to nu_tau appearance
experiment to probe the high sin^2(2theta) and low Delta m^2 region relevant to
explain the atmospheric neutrino anomaly. The experiment relies on a good
identification of quasi-elastic interactions, which is a clean topology that
has an important contribution in the lowest Delta m^2 part of the region
probed. The detector we studied is a fine grained liquid scintillator detector
of 15 kilotons, optimized to detect electrons from tau -> e bar(nu_e) nu_tau
decays, while rejecting backgrounds from pi^0 in nu_mu interactions and
electrons from the nu_e beam contamination. As a reference, the proposed nu_mu
neutrino beam from CERN to Gran Sasso was used.
