Observation of a minimum in collective flow for Ar+V collisions

We have added a new measurement at 100 MeV/nucleon to our previous excitation function for collective flow of light fragments from ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ar}$ ${+}^{51}$V collisions. In the earlier work, flow decreased as the beam energy was raised from 45 to 85 MeV/nucleon. This provided hints to the disappearance of flow, but the lack of measurements at higher beam energies precluded the observation of the reappearance of flow. At a beam energy of 100 MeV/nucleon the flow has reappeared and this allows an experimental determination of the region where attractive scattering balances with repulsive scattering in these collisions. A simultaneous least-squares fit of the flow data for light fragments yields (85±10) MeV/nucleon for the balance energy.