  A fundamental principle of quantum theory, clearly manifested in the two-slit
experiment, is that for any alternatives that cannot be distinguished by
measurement physical predictions are obtained by summation of their amplitudes.
In particle oscillation experiments, a particle's time of detection is not
directly measured, consequently, the detection probability should involve the
summation over amplitudes corresponding to different detection times. However,
in contrast to the principle above, standard treatments involve summation over
probabilities rather than amplitudes; this implicitly assumes the existence of
a decohering mechanism. In this work, we construct the detection probabilities
for particle oscillations by summation over amplitudes, corresponding to
different detection times. The resulting wavelength of particle oscillations
differs from the standard expression by a factor of two. Moreover, we predict a
dependence of the oscillation wavelength on the threshold of the decay process
used for detection.
