Investigation of transverse collective flow of intermediate mass fragments

The transverse flow of intermediate mass fragments (IMFs) has been investigated for the 35 MeV/u ${}^{70}\mathrm{Zn}+{}^{70}\mathrm{Zn}$, ${}^{64}\mathrm{Zn}+{}^{64}\mathrm{Zn}$, and ${}^{64}\mathrm{Ni}+{}^{64}\mathrm{Ni}$ systems. A transition from the IMF transverse flow strongly depending on the mass of the system, in the most violent collisions, to a dependence on the charge of the system, for the peripheral reactions, is shown. This transition was shown to be sensitive to the density dependence of the symmetry energy using the antisymmetrized molecular-dynamics model. The results present an observable, the IMF transverse flow, that can be used to probe the nuclear equation of state. Comparison with the simulation demonstrated a preference for a stiff density dependence of the symmetry energy.

Figure 1

Transverse flow $\stackrel{̲}{\langle \mathit{Px}\rangle }$ for $Z=1$–9 particles in five different centrality bins. Bin 0 (a) represents the most violent collisions, while bin 4 (e) represents the most peripheral. The results are shown for the ${}^{64}\mathrm{Ni}$, ${}^{64}\mathrm{Zn}$, and ${}^{70}\mathrm{Zn}$ systems as shown in the legend.

Figure 2

$R_{\mathrm{flow}}$, as described in Eq. (1), is plotted against the centrality bin number for $Z=6$–9 fragments. The average $R_{\mathrm{flow}}$ value for $Z=4$–9 fragments is shown as the yellow (gray) filled area. The black dashed line represents a perfect transition from $R_{\mathrm{flow}}=1$ for bin 0 to $R_{\mathrm{flow}}=0$ for bin 4. The results from the most peripheral collisions (bin 4) have been excluded due to the increased error.

Figure 3

Average $R_{\mathrm{flow}}$ for $Z=4$–9 fragments ($\langle R_{\mathrm{flow}}\rangle {}_{Z=4–9}$) is plotted as a function of the reduced impact parameter $b_{\mathrm{red}}$ for the experimental data [yellow (grey) filled area] and the AMD-Gemini simulation with both a stiff (red, filled squares) and soft (green, open squares) $E_{\mathrm{sym}}(\rho )$.