Optimal β-beam at the CERN-SPS

A β-beam with maximum γ=150 (for 6He ions) or γ=250 (for 18Ne) could be achieved at the CERN-SPS. We study the sensitivity to θ13 and δ of such a beam as function of γ, optimizing with the baseline constrained to CERN-Frejus (130 km), and also with simultaneous variation of the baseline, for a fixed ion flux. These results are compared to the standard scenario previously considered, with lower γ=60/100, and also with a higher γ∼350 option that requires a more powerful accelerator. We conclude that the sensitivity to CP violation and θ13 increases significantly with γ if the baseline is increased proportionally, while for the CERN-Frejus scenario the dependence on γ is mild provided γ is above 100.