Influence of fast emissions and statistical de-excitation on the isospin transport ratio

TL;DR

This study investigates how fast emissions and statistical de-excitation affect the isospin transport ratio in heavy-ion collisions, revealing that these processes can introduce non-linearities that challenge the ratio's assumed robustness.

Contribution

The paper critically examines the validity of the isospin transport ratio as a probe by analyzing the effects of fast emissions and statistical decay using transport and decay models.

Findings

Statistical de-excitation causes linear transformations at high excitation energies.

Fast emissions introduce non-linear effects on the isospin ratio.

Non-linearities are significant at excitation energies below 2 MeV.

Abstract

Isospin transport ratio is a powerful method to estimate the neutron-proton (n-p) equilibration in heavy-ion collisions, and extensively used to obtain information on the asy-stiffness of the nuclear Equation of State. In fact such a ratio is expected to bypass any perturbations introducing a linear transformation of the chosen observable. In particular, it is supposed to overcome contributions due to emission, either of dynamical or statistical nature, from the primary fragments formed during the collisions. In this paper we explore the validity of this assumption, looking at the quasi-projectile n-p ratio ($N/Z$) in peripheral and semi-peripheral events for Ca+Ca reactions at 35\amev{}, simulated via the Antisymmetrized Molecular Dynamics transport model, coupled to different statistical decay codes. The statistical de-excitation of the primary fragments introduces a linear transformation at relatively high excitation energies (above 2\amev{}) when the residue approaches the Evaporation Attractor Line, while some effect is produced at lower excitation energies due to the occurrence of some non-linearities. As for fast emissions after the end of the projectile-target interaction it is shown that they introduce a non-linear transformation too.