Strangeness production at 1–2 GeV

The production of K+ and K− mesons below and at the NN threshold is summarized, based on a comparison of data with transport model calculations. K+ mesons are created in associate production, together with hyperons (e.g.  Λ ) in multi-step processes involving Δ resonances. These processes occur mainly during the high-density phase of the collision and this makes the K+ an ideal tool to extract the stiffness of the nuclear equation of state, found to be rather soft, with a compressibility modulus K below 240 MeV. In contrast, the major part of K− mesons are produced via strangeness exchange. Most of the created K− are absorbed and the surviving ones are emitted quite late and at low densities.