  Darmstadt $\nu$ oscillations in decay of radioactive ion can only come from
initial state wave function. Causality forbids any influence on transition
probability by detection of $\nu$ or final state interference after decay.
Energy-time uncertainty allows two initial state components with different
energies to decay into combination of two orthogonal states with same energy,
different momenta and different $\nu$ masses. Final amplitudes completely
separated at long times have broadened energy spectra overlapping at short
times. Their interference produces oscillations between Dicke superradiant and
subradiant states having different transition probabilities. Repeated
monitoring by interactions with laboratory environment at regular time
intervals and same space point in laboratory collapses wave function and
destroys entanglement. First-order time dependent perturbation theory gives
probability for initial state decay during small interval between two
monitoring events. Experiment measures momentum difference between two
contributing coherent initial states and obtains information about $\nu$ masses
without detecting $\nu$. Simple model relates observed oscillation to squared
$\nu$ mass difference and gives value differing by less than factor of three
from values calculated from KAMLAND experiment. Monitoring simply expressed in
laboratory frame not easily transformed to other frames and missed in
Lorentz-covariant descriptions based on relativistic quantum field theory.
