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We compare multiplicities as well as rapidity and transverse momentum distributions of protons, pions and kaons calculated within presently available transport approaches for heavy ion collisions around 1 AGeV. For this purpose, three reactions have been selected: Au+Au at 1 and 1.48 AGeV and Ni+Ni at 1.93 AGeV.

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Differential production cross sections of K+/- mesons have been measured in p + C and p + Au collisions at 1.6, 2.5, and 3.5 GeV proton beam energy. At beam energies close to the production threshold, the K- multiplicity is strongly enhanced with respect to proton-proton collisions. According to microscopic transport calculations, this enhancement is caused by two effects: the strangeness exchange reaction NY --> K- NN and an attractive in-medium K- N potential at saturation density.

Within a transport code of BUU type the production of φ mesons in the reactions Ni + Ni at 1.93 A·GeV and Ru + Ru at 1.69 A·GeV is studied. New elementary reaction channels ρN(∆) → φN and πN(1520) → φN are included. In spite of a substantial increase of the φ multiplicities by these channels the results stay below the tentative numbers extracted from experimental data.