High Energy Probes

We review some results on energetic particles production in heavy ion collisions below roughly 100 MeV/A both theoretically and experimentally. We discuss the possibility to gather information about the nuclear Equation Of State (EOS) and viscosity from data. Results on subthreshold pion, energetic photons and nucleons are discussed and contrasted to microscopic models. Important information about the first stages of the reaction are obtained by such probes. At present, we can conclude that we have at least a qualitative understanding of the processes involved when such particles are produced. However, a quantitative understanding of the data and the possibility of understanding deeply the formation mechanism, i.e. incoherent, cooperative or statistical, plus the derivation of important properties of the nuclear EOS are still missing. This calls for new data using more modern detector systems and comparison to more refined microscopic models.