Evidence for Slowly Moving, Highly Excited Nuclear Matter Produced in High-Energy Nucleus-Nucleus Collisions

Abstract

In the reactions 20-GeV Ar + Au and 8-GeV Ne + U, the angular and energy distributions of six nuclei with $Z>~3$ imply approximately isotropic emission from systems moving at ${\ensuremath{\beta}}_{0}\ensuremath{\approx}0.04 \mathrm{to} 0.11$. The invariant cross sections fit either Maxwellians ($\ensuremath{\tau}\ensuremath{\approx}52 \mathrm{to} 65$ MeV) or exponentials in momentum (${P}_{0}\ensuremath{\approx}240 \mathrm{to} 300$ MeV/c) in the moving frame. The low ${\ensuremath{\beta}}_{0}$ and high $\ensuremath{\tau}$ are inconsistent with emission of nuclei ($Z>~3$) from a recoiling fireball unless extreme assumptions are made; they thus imply nonthermal emission.