How two neutrino superbeam experiments do better than one

Abstract We examine the use of two superbeam neutrino oscillation experiments with baselines ≲1000 km to resolve parameter degeneracies inherent in the three-neutrino analysis of such experiments. We find that with appropriate choices of neutrino energies and baselines two experiments with different baselines can provide a much better determination of the neutrino mass ordering than a single experiment alone. Two baselines are especially beneficial when the mass scale for solar neutrino oscillations δm 2 sol is ≳5×10 −5  eV 2 . We also examine CP violation sensitivity and the resolution of other parameter degeneracies. We find that the combined data of superbeam experiments with baselines of 295 and 900 km can provide sensitivity to both the neutrino mass ordering and CP violation for sin 2 2 θ 13 down to 0.03 for | δm 2 atm |≃3×10 −3  eV 2 . It would be advantageous to have a 10% determination of | δm 2 atm | before the beam energies and baselines are finalized, although if | δm 2 atm | is not that well known, the neutrino energies and baselines can be chosen to give fairly good sensitivity for a range of | δm 2 atm |.