Effect of isospin-dependent cluster recognition on the observables in heavy ion collisions

We introduce isospin dependence in the cluster recognition algorithms used in the quantum molecular dynamics model to describe fragment formation in heavy ion collisions. This change reduces the yields of emitted nucleons and enhances the yields of fragments, especially heavier fragments. The enhancement of neutron-rich lighter fragments mainly occurs at midrapidity. Consequently, isospin-dependent observables, such as isotope distributions, yield ratios of $n/p$, $t{/}^3\text{He}$, and isoscaling parameters are affected. We also investigate how equilibration in heavy ion collisions is affected by this change.

Figure 1

(a) Charge distribution of ${}^{124}\text{Sn}{+}^{124}\text{Sn}$ at beam energy of $E/A=50$ MeV for $b=2$ fm for ${\gamma }_i=0.5$. The solid circles are results from the iso-MST algorithm and the the open circles for the same reaction system. (b) $Y\left(\text{iso-MST}\right)/Y\left(\text{MST}\right)$ ratio obtained from the same reaction system.

Figure 2

The rapidity distributions of (a) the neutron yields, (b) the proton yields, (c) the yield ratios, $Y\left(n\right)/Y\left(p\right)$, (d) the $t$ yields, (e) the ${}^3\text{He}$ yields, and (f) the yield ratios, $Y\left(t\right)/Y{(}^3\text{He})$.

Figure 3

Calculated primary isotope yields of Li, Be, B, C, N, and O for ${}^{124}\text{Sn}{+}^{124}\text{Sn}$ with an angular gate of ${70}^{\circ }\le {\theta }_{\text{c.m.}}\le {110}^{\circ }$ for ${\gamma }_i=0.5$ at $b=2$ fm.

Figure 4

$R_{21}$ values obtained from the ratios of the primary isotopic distributions for ${}^{124}\text{Sn}{+}^{124}\text{Sn}$ collisions divided by those for ${}^{112}\text{Sn}{+}^{112}\text{Sn}$ collisions, for ${\gamma }_i=0.5$ at $b=2$ fm. The upper panel shows the results obtained with the iso-MST case for $Z=3$ to 8, and the lower panel shows the results obtained with the MST case for $Z=3$ to 8. The best-fit isoscaling parameters are listed in the panels.

Figure 5

The calculated results of longitudinal (left panel) and transverse (right panel) rapidity distribution for the $Z$-weighted yield ($Z=1$–6) for ${}^{124}\text{Sn}{+}^{124}\text{Sn}$ at $b=2$ fm.