  In the last few years spectacular results have been achieved with the
demonstration of non vanishing neutrino masses and flavour mixing. The ultimate
goal is the understanding of the origin of these properties from new physics.
In this road, the last unknown mixing [Ue3] must be determined. If it is proved
to be non-zero, the possibility is open for Charge Conjugation-Parity (CP)
violation in the lepton sector. This will require precision experiments with a
very intense neutrino source. Here a novel method to create a monochromatic
neutrino beam, an old dream for neutrino physics, is proposed based on the
recent discovery of nuclei that decay fast through electron capture. Such
nuclei will generate a monochromatic directional neutrino beam when decaying at
high energy in a storage ring with long straight sections. We also show that
the capacity of such a facility to discover new physics is impressive, so that
fine tuning of the boosted neutrino energy allows precision measurements of the
oscillation parameters even for a [Ue3] mixing as small as 1 degree. We can
thus open a window to the discovery of CP violation in neutrino oscillations.
