Neutrino beams from electron capture at high gamma

We investigate the potential of a flavor pure high gamma electron captureelectron neutrino beam directed towards a large water cherenkov detector with500 kt fiducial mass. The energy of the neutrinos is reconstructed by theposition measurement within the detector and superb energy resolutioncapabilities could be achieved. We estimate the requirements for such ascenario to be competitive to a neutrino/anti-neutrino running at a neutrinofactory with less accurate energy resolution. Although the requirements turnout to be extreme, in principle such a scenario could achieve as good abilitiesto resolve correlations and degeneracies in the search for sin^2(2 theta_13)and delta_CP as a standard neutrino factory experiment.Comment: 21 pages, 7 figures, revised version, to appear in JHEP, Fig.7 extended, minnor changes, results unchange