Universal Fragment-Momentum Distribution in High-Energy Nucleus-Nucleus Collisions

Abstract

Fragments with $1<~Z<~12$, some with energies as low as 3 MeV/nucleon and some with energies as high as 120 MeV/nucleon, have been analyzed in high-energy nucleus-nucleus reactions with C, Ne, and Ar projectiles. For a given projectile the invariant cross sections of all fragments appear to define a "universal" curve that is exponential in momentum, provided momentum is evaluated in a frame in which the distribution is isotropic. The low speed of the frame (\ensuremath{\sim}0.01c to \ensuremath{\sim}0.1c) suggests emission from the recoiling target.