Fragment multiplicity dependent charge distributions in heavy ion collisions

The dependence of intermediate-mass-fragment (IMF) element distributions on the multiplicity, $N_{\mathrm{IMF}},$ of detected fragments has been measured for ${}^{84}{\mathrm{K}\mathrm{r}+}^{197}\mathrm{Au}$ collisions at $E/A=35\mathrm{}$, 55, 70, 100, 200, and 400 MeV. The observed dependence can be parametrized as ${P(N}_{\mathrm{IMF}}|Z\left)\propto P\right(Z\left)\mathrm{}\exp \right(-c\cdot N_{\mathrm{IMF}}\cdot Z),$ where $c$ is a beam-energy and excitation-energy dependent parameter. Previous work indicated this parameter is zero in the liquid-gas coexistence region and positive in the gaseous phase. In contrast, we observe both negative and positive values for $c$, revealing the meaning of this parameter to be less straightforward than previously assumed. The magnitude of $c$ appears nonetheless to provide a nontrivial test of multifragmentation models.