Disappearance of flow in intermediate-energy nucleus-nucleus collisions

The disappearance of transverse collective flow for ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ar}$ ${+}^{27}$Al collisions is studied with an improved Boltzmann-Uehling-Uhlenbeck equation. For collisions at impact parameters less than 3 fm, the predicted energy of balance, ${\mathit{E}}_{\mathrm{bal}}$, is very sensitive to the in-medium nucleon-nucleon cross section, but insensitive to the equation of state. At larger impact-parameter collisions, the sensitivities to both the in-medium nucleon-nucleon cross section and the equation of state at subnuclear density becomes comparable. Comparisions with experimental data indicate an in-medium nucleon-nucleon cross section in the range of 25–45 mb.