Thermal and Chemical Freeze-out in Spectator Fragmentation

TL;DR

This study investigates the thermal and chemical freeze-out processes in spectator fragmentation by analyzing isotope and excited-state temperatures in gold nucleus collisions, revealing a transition point indicating sequential freeze-out stages.

Contribution

It provides new evidence for a chemical freeze-out occurring before thermal freeze-out in nuclear disintegration processes.

Findings

Isotope temperatures differ from excited-state temperatures at transition.

Transition from residue formation to multi-fragment production identified.

Chemical freeze-out precedes thermal freeze-out in the process.

Abstract

Isotope temperatures from double ratios of hydrogen, helium, lithium, beryllium, and carbon isotopic yields, and excited-state temperatures from yield ratios of particle-unstable resonances in 4He, 5Li, and 8Be, were determined for spectator fragmentation, following collisions of 197Au with targets ranging from C to Au at incident energies of 600 and 1000 MeV per nucleon. A deviation of the isotopic from the excited-state temperatures is observed which coincides with the transition from residue formation to multi-fragment production, suggesting a chemical freeze-out prior to thermal freeze-out in bulk disintegrations.