Probing the nuclear matter equation of state with neutrons from nucleus-nucleus collisions

Abstract

We report the first neutron triple-differential cross-sections measured in multiplicity-selected heavy-ion collisions. We examine the maximum azimuthal anisotropy ratio of these neutron cross-sections from 400 AMeV Nb-Nb and Au-Au collisions as a probe of the nuclear equation of state. Experiment reveals that this ratio does not depend on the mass of the colliding nuclei, contrary to the predictions of the Quantum Molecular Dynamics (QMD) transport theory. We compare the Nb-Nb data also with theoretical calculations done within the Boltzmann-Uehling-Uhlenbeck framework with both momentum-dependent and momentum-independent interactions. We find that the experiment is sensitive to the size of the nuclear incompressibility modulus K in the nuclear matter equation of state, and that the data demand a K value compatible with state-of-the-art nuclear matter calculations.