A low energy optimization of the CERN-NGS neutrino beam for a $\theta_{13}$ driven neutrino oscillation search

The possibility to improve the CERN to Gran Sasso neutrino beam performances for $\theta_{13}$ searches is investigated. We show that by an appropriate optimization of the target and focusing optics of the present CNGS design, we can increase the flux of low energy neutrinos by about a factor 5 compared to the current $\tau$ optimized focalisation. With the ICARUS 2.35 kton detector at LNGS and in case of negative result, this would allow to improve the limit to $\sin^22\theta_{13}$ by an order of magnitude better than the current limit of CHOOZ at $\Delta m^2\approx 3\times 10^{-3} \rm eV^2$ within 5 years of nominal CNGS running. This is by far the most sensitive setup of the currently approved long-baseline experiments and is competitive with the proposed JHF superbeam.