There are two types of scales present simultaneously in the spacelike as well as in the timelike directions in a model class describing a cylindrically symmetric, finite, three-dimensionally expanding boson source. One type of scale is related to the finite lifetime or geometrical size of the system, and the other type is governed by the rate of change of the local momentum distribution in the considered temporal or spatial direction. The parameters of the Bose-Einstein correlation function may obey an ${\mathit{M}}_{\mathit{t}}$ scaling, as observed in S+Pb and Pb+Pb reactions at CERN SPS. This ${\mathit{M}}_{\mathit{t}}$ scaling may imply that the Bose-Einstein correlation functions view only a small part of a large and expanding system. The full sizes of the expanding system at the last interaction are shown to be measurable with the help of the invariant momentum distribution of the emitted particles. A vanishing duration parameter can also be generated, with a specific ${\mathit{M}}_{\mathit{t}}$ dependence, in the considered model class. © 1996 The American Physical Society.

• Received 31 October 1995

DOI:https://doi.org/10.1103/PhysRevC.54.1390