Thermal expansion effects in the 8 GeV/c ${\pi }^{-}{+}^{197}\mathrm{Au}$ reaction

Fragment kinetic energy spectra for reactions induced by 8.0 $\mathrm{GeV}/c{\pi }^{-}$ beams on a ${}^{197}\mathrm{Au}$ target have been analyzed. The average fragment kinetic energies are observed to increase systematically with fragment charge but are nearly independent of excitation energy. Near $E*/A=5\mathrm{}$ MeV, the data are well accounted for by two statistical multifragmentation models, SMM and SIMON-explosion. However, at higher excitation energies, a small amount of extra energy, proportional to the fragment mass, is required in the models in order to match the experimental fragment’s kinetic energies. This extra expansion energy is small relative to the radial expansion observed in heavy-ion-induced reactions, consistent with the interpretation that the latter expansion may be driven primarily by collective dynamical effects that are not present in light-ion-induced collisions.