Alternating ions in a β-beam to solve degeneracies

We study how the eightfold-degeneracy in the (θ13,δ) plane observed in γ∼100β-beams can be reduced by periodically changing the ions in the storage ring. This “ions cocktail” allows to change the neutrino energy, at fixed γ, by choosing ions with different decay energies. We propose to combine the standard 6He and 18Ne beams with 8Li and 8B ones. These latter two ions have peaked νe→νμ oscillation probabilities for γ=100 at a baseline L∼700km. At this distance and this γ the oscillation probability of 6He and 18Ne neutrinos is at its second maximum. This setup is particularly suited for large enough values of θ13 (within reach at T2K-I) and it allows solving most of the eightfold-degeneracy, measuring θ13,δ and the sign of the atmospheric mass difference for values of θ13⩾5°.