  The role of simple quantum mechanics in understanding neutrino oscillation
experiments is pointed out by comparison with two-slit and Bragg scattering
experiments. The importance of considering the beam and the detector as a
correlated quantum system is emphasized. Quantum mechanics alone shows that the
difference observed in the same neutrino detector at Super-Kamiokande between
upward and downward going neutrinos requires the existence of a neutrino mass
difference. The localization of the source and detector in space in the
laboratory system for long times leads to an uncertainty in the momentum but
not of the energy of the neutrino and to coherence between states having
different momenta and the same energy and not between states with different
energies.
