Comparative Study of Multifragmentation of Gold Nuclei Induced by Relativistic Protons, $^4$He, and $^{12}$C

Multiple emission of intermediate-mass fragments has been studied for the collisions of p, 4 He and 12 C on Au with the 4 π setup FASA. The mean IMF multiplicities (for the events with at least one IMF) are saturating at the value of 2 . 2 ± 0 . 2 for the incident energies above 6 GeV. The observed IMF multiplicities cannot be described in a two-stage scenario, a fast cascade followed by a statistical multifragmentation. Agreement with the measured IMF multiplicities is obtained by introducing an intermediate phase and modifying empirically the excitation energies and masses of the remnants. The angular distributions and energy spectra from the p-induced collisions are in agreement with the scenario of “thermal” multifragmentation of a hot and diluted target spectator. In the case of 12 C+Au(22.4 GeV) and 4 He(14.6 GeV)+Au collisions, deviations from a pure thermal break-up are seen in the energy spectra of the emitted fragments, which are harder than those both from model calculations and from the measured ones for p-induced collisions. This difference is attributed to a collective flow.