  A study of Bose-Einstein correlations in pairs of identically charged pions
produced in e+e- annihilations at the Z0 peak has been performed for the first
time assuming a non-static emitting source. The results are based on the high
statistics data obtained with the OPAL detector at LEP. The correlation
functions have been analyzed in intervals of the average pair transverse
momentum and of the pair rapidity, in order to study possible correlations
between the pion production points and their momenta (position-momentum
correlations). The Yano-Koonin and the Bertsch-Pratt parameterizations have
been fitted to the measured correlation functions to estimate the geometrical
parameters of the source as well as the velocity of the source elements with
respect to the overall centre-of-mass frame. The source rapidity is found to
scale approximately with the pair rapidity, and both the longitudinal and
transverse source dimensions are found to decrease for increasing average pair
transverse momenta.
