Entropy Production at High Energy and mu_B

The systematics of bulk entropy production in experimental data on A+A, p+p and e+e- interactions at high energies and large mu_B is discussed. It is proposed that scenarios with very early thermalization, such as Landau's hydrodynamical model, capture several essential features of the experimental results. It is also pointed out that the dynamics of systems which reach the hydrodynamic regime give similar multiplicities and angular distributions as those calculated in weak-coupling approximations (e.g. pQCD) over a wide range of beam energies. Finally, it is shown that the dynamics of baryon stopping are relevant to the physics of total entropy production, explaining why A+A and e+e- multiplicities are different at low beam energies.