Collisions of Au on Au at incident energies of 150, 250 and 400 A MeV were studied with the FOPI-facility at GSI Darmstadt. Nuclear charge (Z ≤ 15) and velocity of the products were detected with full azimuthal acceptance at laboratory angles 1 • ≤ θ lab ≤ 30 • . Isotope separated light charged particles were measured with movable multiple telescopes in an angular range of 6 − 90 • . Central collisions representing about 1% of the reaction cross section were selected by requiring high total transverse energy, but vanishing sideflow. The velocity space distributions and yields of the emitted fragments are reported. The data are analysed in terms of a thermal model including radial flow. A comparison with predictions of the Quantum Molecular Model is presented.PACS: 25.70.Pq

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The incident energy at which the azimuthal distributions in semi-central heavy ion collisions change from in-plane to out-of-plane enhancement -E tran is studied as a function of mass of emitted particles, their transverse momentum and centrality for Au+Au collisions. The analysis is performed in a reference frame rotated with the sidewards flow angle (Θ f low ) relative to the beam axis.A systematic decrease of E tran as function of mass of the reaction products, their transverse momentum and collision centrality is evidenced.The predictions of a microscopic transport model (IQMD) are compared with the experimental results.