NEUTRONS FROM MULTIPLICITY-SELECTED AU-AU COLLISIONS AT 150A, 250A, 400A, AND 650A MEV

We measured neutron triple-differential cross sections from multiplici ty-selected Au-Au collisions at 150A, 250A, 400A, and 650A MeV. The re action plane for each collision was estimated from the summed transver se velocity vector of the charged fragments emitted in the collision. We examined the azimuthal distribution of the triple-differential cros s sections as a function of the polar angle and the neutron rapidity. We extracted the average in-plane transverse momentum [P-x] and the no rmalized observable [P-x/P-perpendicular to], where P-perpendicular to is the neutron transverse momentum, as a function of the neutron cent er-of-mass rapidity, and we examined the dependence of these observabl es on beam energy. These collective flow observables for neutrons, whi ch are consistent with those of protons plus bound nucleons from the P lastic Ball Group, agree with the Boltzmann Uehling-Uhlenback (BUU) ca lculations with a momentum-dependent interaction. Also, we calculated the polar-angle-integrated maximum azimuthal anisotropy ratio R from t he value of [P-x/P-perpendicular to].