  Back-to-Back Correlations (BBC) of particle-antiparticle pairs are predicted
to appear if hot and dense hadronic matter is formed in high energy
nucleus-nucleus collisions. The BBC are related to in-medium mass-modification
and squeezing of the quanta involved. Although the suppression of finite
emission times were already known, the effects of finite system sizes and of
collective phenomena had not been studied yet. Thus, for testing the survival
and magnitude of the effect in more realistic situations, we study the BBC when
mass-modification occurs in a finite sized, thermalized medium, considering a
non-relativistically expanding fireball with finite emission time, and
evaluating the width of the back-to-back correlation function. We show that the
BBC signal indeed survives the expansion and flow effects, with sufficient
magnitude to be observed at RHIC.
