Abstract
>A review of meson emission in heavy ion collisions at incident energies around 1 -- 2 A\cdotGeV is presented. It is shown how the shape of the spectra and the various particle yields vary with system size, with centrality and with incident energy. A statistical model assuming thermal and chemical equilibrium and exact strangeness conservation (i.e. strangeness conservation per collision) explains most of the observed features.
Emphasis is put onto the study of K^+ and K^- emission. In the framework of this statistical model it is shown that the experimentally observed equality of K^+ and K^- rates at threshold corrected energies \sqrt{s} - \sqrt{s_{th}} is due to a crossing of two excitation functions. Furthermore, the independence of the K^+ to K^- ratio on the number of participating nucleons observed between 1 and 10 A\cdotGeV is consistent with this model. The observed flow effects are beyond the scope of this model.