Neutrons from multiplicity-selected La-La and Nb-Nb collisions at400A MeVand La-La collisions at250A MeV

Abstract

Triple-differential cross sections for neutrons from high-multiplicity La-La collisions at 250 and 400 MeV per nucleon and Nb-Nb collisions at 400 MeV per nucleon were measured at several polar angles as a function of the azimuthal angle with respect to the reaction plane of the collision. The reaction plane was determined by a transverse-velocity method with the capability of identifying charged-particles with $Z=1,$ $Z=2,$ and $Z>2.$ The flow of neutrons was extracted from the slope at mid-rapidity of the curve of the average in-plane momentum vs the center-of-mass rapidity. The squeeze-out of the participant neutrons was observed in a direction normal to the reaction plane in the normalized momentum coordinates in the center-of-mass system. Experimental results of the neutron squeeze-out were compared with BUU calculations. The polar-angle dependence of the maximum azimuthal anisotropy ratio $r(\ensuremath{\theta})$ was found to be insensitive to the mass of the colliding nuclei and the beam energy. Comparison of the observed polar-angle dependence of the maximum azimuthal anisotropy ratio $r(\ensuremath{\theta})$ with BUU calculations for free neutrons revealed that $r(\ensuremath{\theta})$ is insensitive also to the incompressibility modulus in the nuclear equation of state.