We consider a β-Beam facility where 8 Li and 8 B ions are accelerated at γ = 350, accumulated in a 10 Km storage ring and let decay, so as to produce intenseν e and ν e beams. These beams illuminate two magnetized iron detectors located at L ≃ 2000 Km and L ≃ 7000 Km, respectively. The physics potential of this setup is analysed in full detail as a function of the flux. We find that, for the highest flux considered (10 × 10 18 ion decays per year per baseline), the sensitivity to θ 13 reaches sin 2 2θ 13 ≥ 1 × 10 −4 ; the sign of the atmospheric mass difference can be identified, regardless of the true hierarchy, for sin 2 2θ 13 ≥ 3 × 10 −4 ; and, CP violation can be discovered in 70% of the δ-parameter space for sin 2 2θ 13 ≥ 10 −3 , having some sensitivity to CP violation down to sin 2 2θ 13 ≥ 2 × 10 −4 for |δ| ∼ 90 • .
IntroductionThe • ; for the leptonic CP-violating phase δ we have no information whatsoever (see, however, Ref. [20]). We have no clue on the ordering of the neutrino mass eigenstates, either, i.e. on the sign of the atmospheric mass difference ∆m 2 atm (of which only the absolute value has been measured). It must be stressed that neutrinos being hierarchically ordered (∆m The full understanding of the leptonic mixing matrix constitutes, together with the discrimination of the Dirac/Majorana character of neutrinos and with the measurement of their absolute mass scale, the main neutrino-physics goal for the next decade. In the recent past, most of the experimental breakthroughs in neutrino physics have been achieved by exploiting the so-called "disappearance channels": by observing a deficit in the neutrinos that reach the detector with respect to those expected to be emitted from the source, a positive and eventually unambiguous signal of neutrino oscillations has been established. New-generation experiments have been proposed to look for the fleeting and intimately related parameters θ 13 and δ through "appearance channels" such as ν e ↔ ν µ (the "golden channel") [22] and ν e → ν τ (the "silver channel") [23]. However, strong correlations between θ 13 and δ [24] and the presence of parametric degeneracies in the (θ 13 , δ) parameter space, [25]-[27], make the simultaneous measurement of the two variables extremely difficult. A further problem arises from our present imprecise knowledge of atmospheric parameters, whose uncertainties are far too large to be neglected when looking for such tiny signals as those expected in appearance experiments [28].Most of the proposed solutions to these problems imply the combination of different experiments and facilities, such as reactors (Double Chooz [29] should start data taking in 2008), Super-Beams (of which T2K [30] is the first approved one), β-Beams [31] or the Neutrino Factory [32,33]. To compare different options and to understand which of them is the one to be pursued as a future neutrino facility, a list of observables to be measured has been defined: θ 13 ; the CP-violating phase δ; the sign of the atmospheric mass difference (hereaft...