Cold breakup of spectator residues in nucleus-nucleus collisions at high energy

Abstract

Inclusive data from fragmentation reactions of the type $A_P+A_T\to Z+X$ are analyzed and a reaction mechanism is proposed. A projectile $A_P (\mathrm{p}, \mathrm{He}, \alpha , or \mathrm{Ne})$ collides with a target nucleus $A_T$ (Au) and one fragment with charge $Z$ and energy $E$ is observed at a solid angle $\Omega$. Projectile energies vary between $84A$ MeV and several $A$ GeV. We propose a parametrization for the triple differential cross section $\frac{d^3\sigma }{d\Omega }\mathrm{dE}\mathrm{dZ}$ with six free parameters. The parametrization generalizes the two-vector model which is often used to describe spallation products in proton-nucleus collisions. By fitting data from various experiments we establish a systematics of the six parameters. The experimental values of the parameters can be quantitatively understood in a model where the target nucleus breaks into several fragments similar to the shattering of glass.