Multifragmentation of the remnant produced in the reaction of $1A$ GeV gold with carbon

A high-statistics exclusive study of the multifragmentation of $1A$ GeV gold on carbon has been performed. Particles with $Z<~2$ show evidence of emission in a first prompt stage as well as in a second equilibrium stage whereas fragments with $Z>~3$ appear to be emitted essentially only in the second stage. Two methods for the separation of the $Z<~2$ particles into the two stages are given and they are in agreement. The yields for each stage are determined as a function of the event charged particle multiplicity $m$. The mass, nuclear charge, excitation energy per nucleon, and temperature of the remnant left after the first stage and their fluctuations have been determined as a function of $m$. The expansion of the remnant to fragment freeze-out is examined. The freeze-out temperature is determined from double isotope ratios as a function of $m$ and isentropic trajectories are obtained in the temperature-density plane. The caloric curve shows a monotonic increase with excitation energy. Some of the energy is in the form of radial flow. Overall, the results are consistent with a previous statistical analysis of the data which suggests that, over a certain range of excitation energies, multifragmentation involves a continuous phase transition.