Properties of an equilibrium hadron gas subjected to the adiabatic   longitudinal expansion
  We consider an ideal gas of massive hadrons in thermal and chemical equilibrium. The gas expands longitudinally in an adiabatic way. This evolution for a baryonless gas reduces to a hydrodynamic expansion. Cooling process is parametrized by the sound velocity. The sound velocity is temperature dependent and is strongly influenced by hadron mass spectrum. 
Dariusz Prorok and Ludwik Turko