CP violation and mass hierarchy at medium baselines in the large theta(13) era

The large value of θ 13 recently measured by rector and accelerator experiments opens unprecedented opportunities for precision oscillation physics. In this paper, we reconsider the physics reach of medium baseline superbeams. For θ 13≃9∘ we show that facilities at medium baselines—i.e. \(L \simeq \mathcal{O}\) (1000 km)—remain optimal for the study of CP violation in the leptonic sector, although their ultimate precision strongly depends on experimental systematics. This is demonstrated in particular for facilities of practical interest in Europe: a CERN to Gran Sasso and CERN to Phyasalmi ν μ beam based on the present SPS and on new high power 50 GeV proton driver. Due to the large value of θ 13, spectral information can be employed at medium baselines to resolve the sign ambiguity and determine the neutrino mass hierarchy. However, longer baselines, where matter effects dominate the ν μ →ν e transition, can achieve much stronger sensitivity to \(\operatorname{sign}(\Delta m^{2})\) even at moderate exposures.