Disappearance of flow and its relevance to nuclear matter physics

Light charged fragments from the reaction ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ar}$ ${+}^{51}$V at 35–85 MeV/nucleon in 10 MeV/nucleon steps have been measured with a 4π detector. The observed transverse collective momentum in central collisions decreases monotonically from 45 to 85 MeV/nucleon. The data are interpreted assuming that the attractive mean-field deflects the fragments to negative scattering angles. As the beam energy is raised, the attractive scattering is opposed by the buildup of compressed nuclear matter. A lower limit of 76 MeV/nucleon is placed on the beam energy where the attractive deflection is balanced by the repulsive side-splash mechanism. The results are compared to theoretical predictions and it is demonstrated the predictions are sensitive to two aspects of nuclear matter physics: the in-medium nucleon-nucleon cross section and the nuclear compressibility.