The 2+2 and 3+1 four-family neutrino mixing at the neutrino factory

Abstract.

We upgrade the study of the physical reach of a neutrino factory in the four-family neutrino mixing scenario, taking into account the latest LSND results, which point out how the 3+1 scheme cannot be completely ruled out within the present experimental data (although the 2+2 scheme is still the preferred choice when four neutrinos are considered). A detailed comparison of the physical reach of the $\nu$ factory in the two schemes is given, with similar results for the sensitivity to the mixing angles. Huge CP-violating effects can be observed in both schemes with a near, O(10) km, detector of O(10) kton size in the $\nu_\mu \to \nu_\tau$ channel. A smaller detector of 1 kton size can still observe very large effects in this channel.