The Origin of the Difference between Multiplicities in e+e- Annihilation   and Heavy Ion Collisions
  Multiplicities in e+e- annihilation and relativistic heavy ion collisions show remarkable similarities at high energies. A thermal-statistical model is proposed to explain the differences which occur mainly at low beam energies. Two different calculations are performed, one using an approximate thermodynamic relationship, the other using a full thermal model code. The results are in qualitative agreement, suggesting that the interplay of baryon density and temperature tends to systematically suppress the total multiplicity at lower beam energies. 
J. Cleymans, M. Stankiewicz, P. Steinberg, S. Wheaton