  Deviations from thermal distribution functions of produced particles in
relativistic heavy-ion collisions are discussed as indicators for
nonequilibrium processes. The focus is on rapidity distributions of produced
charged hadrons as functions of collision energy and centrality which are used
to infer the fraction of produced particles from a central fireball as compared
to the one from the fragmentation sources that are out of equilibrium with the
rest of the system. Overall thermal equilibrium would only be reached for large
times t -> infinity.
