Quantum Mechanics of Neutrino Detectors Determine Coherence and Phases in Oscillation Experiments

The apparent symmetry between energy and momentum found in all covariant descriptions of neutrino oscillations is destroyed in the neutrino detector, a quantum mechanical system described by a density matrix diagonal in energy but not in momentum. The off diagonal matrix elements between states of different momenta and the same energy produce the coherence and interference between mass eigenstates having the same energy and different momenta that produce oscillations.