The silver channel at the Neutrino Factory

We notice that looking for ${\nu }_e\to {\nu }_{\tau }$ at the same time as $\nu_e \to \nu_\mu$ oscillations could significantly help to reduce the errors in the leptonic CP-violating phase $\delta$ measurement. We show how the $\nu_e \to \nu_\mu$(\mathrm{‘}\mathrm{‘}golde{n}^{\mathrm{\prime }\mathrm{\prime }})and$\nu_e \to \nu_\tau$ (``silver’') transitions observed at an OPERA-like 2 Kton lead-emulsion detector at L = 732 Km, in combination with the ${\nu }_e\to {\nu }_{\mu }$ transitions observed at a 40 Kton magnetized iron detector with a baseline of L = 3000 Km, strongly reduce the so-called $({\theta }_{13},\delta )$ ambiguity. We also show how a moderate increase in the OPERA-like detector mass (4 Kton instead of 2 Kton) completely eliminates the clone regions even for small values of ${\theta }_{13}$.