De-excitation effects in multi-nucleon transfer reactions

TL;DR

The paper addresses how nuclear fragment de-excitation shapes observable outcomes in multi-nucleon transfer (MNT) reactions. It develops a hybrid approach, TDCDFT+GEMINI, that couples time-dependent covariant density-functional theory dynamics with the GEMINI++ statistical de-excitation model, extracting primary fragment distributions via particle-number projection and feeding these into a cascade of decays. Key findings show that including de-excitation improves agreement with experimental cross sections for several channels, reveals an abrupt opening of new channels around $E_{\text{lab}}$ near $256$ MeV accompanied by a rise in Shannon entropy, and demonstrates a substantial loss of PLF–TLF mutual information due to neutron evaporation, especially in central collisions. The work thereby bridges microscopic collision dynamics and final-state observables, highlighting de-excitation as a crucial factor in both yield distributions and quantum correlation erosion, with implications for interpreting MNT experiments.

Abstract

This study quantifies the impact of nuclear de-excitation on correlations in multi-nucleon transfer (MNT) reactions. To bridge the gap between initial collision dynamics and final experimental observables, we introduce a hybrid TDCDFT+GEMINI approach, integrating time-dependent covariant density functional theory (TDCDFT) with the statistical de-excitation model GEMINI++. Applied to the $^{40}$Ca + $^{208}$Pb reaction, our method demonstrates that the de-excitation is essential for reconciling theoretical cross sections with experimental data. Analysis of the cross-section Shannon entropy reveals that new reaction channels open abruptly at a specific energy threshold. By employing mutual information, we show that the de-excitation process significantly degrades the initial quantum entanglement between the projectile-like and the target-like fragments, revealing a key mechanism through which fundamental quantum correlations are lost.

Figures (5)

• Figure 1: Cross sections for the projectile-like fragments in the $^{40}$Ca + $^{208}$Pb reaction at $E_{\text{lab}}=249$ MeV. Each panel shows the cross sections for a different proton-transfer channel, as a function of the PLF neutron number (horizontal axis). Dots (red) denote the experimental values SSzilner2005PRC. Histograms (pink) present TDCDFT results for primary reaction products, and blue solid lines denote the TDCDFT+GEMINI results for secondary reaction products. For comparison, the TDHF+GEMINI results Sekizawa2017PRC are also shown (green shaded histograms).
• Figure 2: Distribution of cross sections for primary (a)-(f) and secondary (g)-(l) fragments produced in the reaction $^{40}$Ca + $^{208}$Pb, at incident energies between 235 and 270 MeV.
• Figure 3: Cross-section Shannon entropy for primary (black squares) and secondary (red circles) fragments in the reaction $^{40}$Ca + $^{208}$Pb, as a function of the incident energy.
• Figure 4: Joint probability distribution of the PLF and TLF following the fragment de-excitation in the $^{40}$Ca + $^{208}$Pb reaction at $E_{\text{lab}}$ = 249 MeV, as functions of the impact parameter, for the neutron number in the upper panels (a)-(f), and the number of protons in the lower panels (g)-(l).
• Figure 5: Mutual information between the PLF and the TLF for (a) the number of neutrons, and (b) number of protons, as functions of the impact parameter. The values of mutual information before and after the de-excitation are denoted by circles (black) and squares (red), respectively, connected by solid lines. The corresponding Shannon entropies after the de-excitation for the PLF (green dot-dashed), the TLF (orange dot-dashed), and their joint probability (blue dashed) are also plotted.