Proton-helium correlation in 94 MeV/nucleoninduced16reactions on Al, Ni, and Au targets

Azimuthal distributions of helium ions have been measured in coincidence with high-energy protons in reactions induced by ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ at 94 MeV/nucleon on ${}_{}{}^{27}{}_{}{}^{}\mathrm{Al}$, ${}_{}{}^{58}{}_{}{}^{}\mathrm{Ni}$, and ${}_{}{}^{197}{}_{}{}^{}\mathrm{Au}$. Helium ions have been detected in a large area multidetector. Protons have been observed at 90°. Mean multiplicities of light charged particles (H and He) are found slightly dependent on the target mass. Strong azimuthal asymmetries whose intensity is larger for the Al target and vanishes with the increasing of the target mass are observed in the He distributions. Experimental data are discussed in the framework of the participant-spectator picture of a modified fireball model, taking into account intermediate energy corrections. In this framework the behavior of the azimuthal asymmetries, as a function of the target mass, indicates a strong final-state interaction between participant and spectator fragments. Such a result is found in agreement with interaction time predictions of a microscopical calculation based on the Boltzmann-Nordheim-Vlasov equation.