Quasiprojectile breakup and isospin equilibration at Fermi energies: an indication of longer projectile-target contact times?

TL;DR

This study investigates quasiprojectile breakup and isospin equilibration in Ni+Ni collisions at Fermi energies, suggesting longer projectile-target contact times in breakup channels based on experimental data and AMD-GEMINI++ simulations.

Contribution

It provides new insights into the relationship between quasiprojectile breakup, isospin diffusion, and contact times, supported by experimental and simulation data.

Findings

Higher isospin relaxation in breakup channels compared to binary channels.

Longer projectile-target contact times are associated with breakup channels.

Model calculations support the link between contact time and breakup phenomena.

Abstract

An investigation of the quasiprojectile breakup channel in semiperipheral and peripheral collisions of $^{58,64}$Ni+$^{58,64}$Ni at 32 and 52 MeV/nucleon is presented. Data have been acquired in the first experimental campaign of the INDRA-FAZIA apparatus in GANIL. The effect of isospin diffusion between projectile and target in the two asymmetric reactions has been highlighted by means of the isospin transport ratio technique, exploiting the neutron-to-proton ratio of the quasiprojectile reconstructed from the two breakup fragments. We found evidence that, for the same reaction centrality, a higher degree of relaxation of the initial isospin imbalance is achieved in the breakup channel with respect to the more populated binary output, possibly indicating the indirect selection of specific dynamical features. We have proposed an interpretation based on different average projectile-target contact times related to the two exit channels under investigation, with a longer interaction for the breakup channel. The time information has been extracted from AMD simulations of the studied systems coupled to GEMINI++: the model calculations support the hypothesis hereby presented.