Conceptual study of an "anti-tagged" experiment searching for $\nu _\mu \to \nu _e$ oscillation

We study the feasibility, from the conceptual point of view, %of a high energy, appearance , zero background experiment to detect %$\nu_\mu \rightarrow \nu_e$ oscillations with maximum sensitivity % ($sin^2 2 \theta = 10^{-4}$) %in the $\Delta m^2 \simeq 1 \; eV^2$ region, %fully covering the area where the LSND experiment claims evidence. Partial %overlap with the atmospheric neutrino region ($\Delta m^2 \simeq 0.01 \; eV^2$ %at maximum mixing) is also foreseen. The ``natural'' $\nu_e$ %background of the neutrino beam, due to $K,\mu$ decays in the decay tunnel, % is controlled by using % a hadron blind detector that vetoes , by time concidence, an eventual %$\nu_e$ signal in %the neutrino detector ({\sl anti-tagging technique}). %The existing CERN PS beamline could be resurrected %because of the ideal $L/E$ ratio and the proton availability before the %LHC era. %----- %We study the feasibility, from the conceptual point of view, %of a high energy, zero background appearance experiment to detect %$\nu_\mu \rightarrow \nu_e$ oscillations with maximum sensitivity %in the $\dm2 \simeq 1 \; eV^2$ region, %fully covering the area where the LSND experiment claims evidence and also %partially overlapping the atmospheric neutrino region. The ``natural'' $\nu_e$ %background of the neutrino beam, due to K and $\mu$ decays in the decay tunnel, %is suppressed by a hadron blind detector that vetoes, by time coincidence, %a possible $\nu_e$ signal in the neutrino detector %({\sl anti-tagging technique}). %The PS accelerator at CERN offers the ideal $L/E$ ratio and %the proton availability before the LHC era. %----- We study the conceptual feasibility of a high energy, ``short baseline'', zero background experiment to search for \numtonue\ oscillations and fully covering the area where the LSND experiment claims evidence. The natural \nue\ background of the \num\ beam, from $K$ and $\mu$ decays in the decay tunnel, is suppressed by a hadron blind detector that vetoes, by time coincidence, a possible \nue\ signal in the neutrino detector ({\sl anti-tagging technique}). We discuss this new idea and we study a possible implementation in the old neutrino line of the PS accelerator, which at CERN offers the ideal $L/E$ ratio. In the anti-tagged \num\ beam, the \nue\ contamination can be reduced by more than two orders of magnitude over conventional beams, down to $\nue/\num = 5\cdot 10^{-5}$. In an ideal appearance experiment using a $300\; t$ detector one would expect after two years $112$ events according to the LSND result, with a background of $1.1\div 2.4$ events. In case of a negative search, the $90\%$ C.L. upper limit in the mixing angle would be $\sin2tme < 1.8\cdot 10^{-4}$ for large \dm2\ and $\dm2 <3.3\cdot 10^{-2}\; eV^2$ for maximal mixing.