Fragment Flow in Au+Au Collisions

Exclusive measurements have been made of Au $+$Au reactions with beam energies ranging from 0.25 $A$ to 1.15 $A$ GeV. We present measurements of directed collective flow averaged over all light fragments with masses up to alphas, as well as separate measurements for protons, deuterons, tritons, ${}^3$He, ${}^4$He, and Li. The results show a strong increase of the directed flow with fragment mass at all energies measured. Experimental results are compared with a quantum molecular dynamics model. We find that neither the “soft” nor the “hard” equation of state can describe the data over the entire range of beam energies.