Optimization of the Neutrino Factory, revisited

We perform the baseline and energy optimization of the Neutrino Factory including the latest simulation results on the magnetized iron detector (MIND). We also consider the impact of τ decays, generated by νμ → ντ or νe → ντ appearance, on the mass hierarchy, CP violation, and θ13 discovery reaches, which we find to be negligible for the considered detector. For the baseline-energy optimization for small sin2 2θ13, we qualitatively recover the results with earlier simulations of the MIND detector. We find optimal baselines of about 2500km to 5000km for the CP violation measurement, where now values of Eμ as low as about 12 GeV may be possible. However, for large sin2 2θ13, we demonstrate that the lower threshold and the backgrounds reconstructed at lower energies allow in fact for muon energies as low as 5 GeV at considerably shorter baselines, such as FNAL-Homestake. This implies that with the latest MIND analysis, low-and high-energy versions of the Neutrino Factory are just two different versions of the same experiment optimized for different parts of the parameter space. Apart from a green-field study of the updated detector performance, we discuss specific implementations for the two-baseline Neutrino Factory, where the considered detector sites are taken to be currently discussed underground laboratories. We find that reasonable setups can be found for the Neutrino Factory source in Asia, Europe, and North America, and that a triangular-shaped storage ring is possible in all cases based on geometrical arguments only.