Study of a Long Baseline $\nu_{\tau}$ Appearance Neutrino Oscillation Experiment in the Quasi-Elastic Regime

We present a study for a design of a long baseline $\nu_{\mu} \rightarrow \nu_{\tau}$ appearance experiment to probe the high $\sin^22\theta$ 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 $\tau\rightarrow{\rm e}\bar{\nu}_{\rm e}\nu_{\tau}$ decays, while rejecting backgrounds from $\pi^0$ in $\nu_{\mu}$ interactions and electrons from the $\nu_{\rm e}$ beam contamination. As a reference, the proposed $\nu_{\mu}$ neutrino beam from CERN to Gran Sasso was used.