Toward CP-even Neutrino Beam
  The best method of measuring CP violating effect in neutrino oscillation experiments is to construct and use a neutrino beam made of an ideal mixture of $\bar{\nu}_e$ and $\nu_e$ of monochromatic lines. The conceptual design of such a beam is described, together with how to measure the CP-odd quantity. We propose to exploit an accelerated unstable hydrogen-like heavy ion in a storage ring, whose decay has both electron capture and bound beta decay with a comparable fraction. 
A. Fukumi, I. Nakano, H. Nanjo, N. Sasao, S. Sato, and M. Yoshimura