Limits of energy equilibration in central Au on Au collisions in the projectile energy range from 150 AMeV to 1050 AMeV

Central collisions of Au on Au were studied with the FOPI-facility at SIS/GSI Darmstadt with emphasis of the data from the forward plastic wall covering laboratory angles 1o≤Θlab≤30o with full azimuthal acceptance. The obtained fragment charge distributions and particle multiplicities were analyzed in terms of a modified statistical model which considers preequilibrium emission prior thermalization. The analysis was extended to isotopic yield ratios simultaneously measured with ΔE/E telescopes. In the model calculations the available c.m. energy is shared among preequilibrium emission, radial flow, thermal excitation and pion production. The comparison of data and simulations indicate an equilibrated source of low thermodynamic temperature and reduced size as well as the dominance of preequilibrium emission with increasing beam energy. (authors)