Isospin Dependence of Incomplete Fusion Reactions at $25\mathrm{MeV}/\mathrm{\text{Nucleon}}$

${}^{40}\mathrm{Ca}+{}^{40,48}\mathrm{Ca},{}^{46}\mathrm{Ti}$ reactions at $25\mathrm{MeV}/\mathrm{\text{nucleon}}$ have been studied using the $4\pi$ CHIMERA detector. An isospin effect on the competition between fusionlike and binarylike reaction mechanisms has been observed. The probability of producing a heavy residue is lower in the case of $N\approx Z$ colliding systems as compared to the case of reactions induced on the neutron rich ${}^{48}\mathrm{Ca}$ target. Predictions based on constrained molecular dynamics II calculations show that the competition between fusionlike and binary reactions in the selected centrality bins can constrain the parametrization of the symmetry energy and its density dependence in the nuclear equation of state.

Figure 1

Mass $m_1$ versus velocity $v_1$ of the largest fragment detected in the ${}^{40}\mathrm{Ca}+{}^{48}\mathrm{Ca}$ (a), ${}^{40}\mathrm{Ca}+{}^{46}\mathrm{Ti}$ (b), and ${}^{40}\mathrm{Ca}+{}^{40}\mathrm{Ca}$ (c) reactions. (d) Projections on the mass axis for ${}^{48}\mathrm{Ca}$ target (full line) ${}^{46}\mathrm{Ti}$ target (dashed line), and ${}^{40}\mathrm{Ca}$ target (dotted line). (e) Charged particle multiplicity in the reactions ${}^{40}\mathrm{Ca}+{}^{48}\mathrm{Ca}$ (dotted histogram) and ${}^{40}\mathrm{Ca}+{}^{46}\mathrm{Ti}$ (shaded area histogram).

Figure 2

Dot histograms: Probability plots of $m_1-m_2$ and $m_1$ normalized to the total mass for the studied reactions. Shaded histogram: $\mathrm{CoMD}\mathrm{\text{−}}\mathrm{II}+\mathrm{GEMINI}$ calculations. See text for details.

Figure 3

$\mathrm{CoMD}\mathrm{\text{−}}\mathrm{II}+\mathrm{GEMINI}$ calculations (shaded area histogram) and experimental results (dotted histograms) for the ${}^{48}\mathrm{Ca}$ case for (a),(b) Stiff1 parametrization; (c),(d) Soft parametrization; (e),(f) Stiff2 parametrization, dashed line CoMD-II calculations, without the Gemini stage.