How two neutrino superbeam experiments do better than one

We examine the use of two superbeam neutrino oscillation experiments with baselines $\lsim 1000$ km to resolve parameter degeneracies inherent in the three-neutrino analysis of such experiments. We find that with appropriate choices of neutrino energy and baseline 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 $\delta m^2_{\rm sol}$ is $\gsim 5\times10^{-5}$ 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 $\sin^22\theta_{13}$ down to 0.03 for $\delta m^2_{\rm atm} \simeq 3\times10^{-3}$ eV$^2$. It would be highly advantageous to have a 10% determination of $|\delta m^2_{\rm atm}|$ before the beam energy and baseline are finalized.