  In the late stage of the evolution of a pion system in high-energy heavy-ion
collisions when pions undergo multiple scatterings, the quantum transport of
the interfering pair of identical pions plays an important role in determining
the characteristics of the Hanbury-Brown-Twiss (HBT) interference. We study the
quantum transport of the interfering pair using the path-integral method, in
which the evolution of the bulk matter is described by relativistic
hydrodynamics while the paths of the two interfering pions by test particles
following the fluid positions and velocity fields. We investigate in addition
the effects of secondary pion sources from particle decays, for nuclear
collisions at AGS and RHIC energies. We find that quantum transport of the
interfering pair leads to HBT radii close to those for the chemical freeze-out
configuration. Particle decays however lead to HBT radii greater than those for
the chemical freeze-out configuration. As a consequence, the combined effects
give rise to HBT radii between those extracted from the chemical freeze-out
configuration and the thermal freeze-out configuration. Proper quantum
treatments of the interfering pairs in HBT calculations at the pion multiple
scattering stage are important for our understanding of the characteristics of
HBT interferometry in heavy-ion collisions.
