  Medium modifications of parton fragmentation provide a novel tomographic tool
for the study of the hot and dense matter created in ultrarelativistic
nucleus-nucleus collisions. Their quantitative analysis, however, is
complicated by the strong dynamical expansion of the collision region. Here, we
establish for the multiple scattering induced gluon radiation spectrum a
scaling law which relates medium effects in a collision of arbitrary dynamical
expansion to that in an equivalent static scenario. Based on this scaling, we
calculate for typical kinematical values of the RHIC and LHC heavy ion programs
medium-modified parton fragmentation functions for heavy ion collisions with
realistic dynamical expansion.
