Isospin blocking and its effects in heavy-ion collisions

TL;DR

This paper introduces the concept of isospin blocking in heavy-ion collisions, showing that high local symmetry energy can hinder isospin diffusion and affect particle ratios, with implications for nuclear matter studies.

Contribution

It proposes and demonstrates the phenomenon of isospin blocking, a new effect where high symmetry energy prevents isospin diffusion in heavy-ion collisions.

Findings

Isospin blocking occurs when local symmetry energy is large.

High symmetry energy reduces isospin asymmetry diffusion.

Isospin blocking influences the $ ext{π}^-/ ext{π}^+$ ratio in collisions.

Abstract

A concept of \emph{isospin blocking} in the process of isospin diffusion in heavy-ion collisions is raised. Generally, in the process of isospin diffusion, isospin asymmetry would diffuse from the place with large asymmetry to the place with small asymmetry. However, our study shows that the isospin diffusion could be blocked in case the local value of the symmetry energy is larger. We dub this phenomenon ``isospin blocking''. To check this behavior, in the framework of an Isospin-dependent Boltzmann-Uehling-Uhlenbeck (IBUU) transport model, isospin diffusions in the isotope Sn+Sn reactions at 270 MeV/nucleon are studied. It is shown that the value of the after-diffusion asymmetry is distinctly blocked if the local symmetry energy is large. The effects of the isospin blocking on the isospin asymmetry of dilute and dense matter and the final $\pi^-/\pi^+$ ratio in heavy ion collisions are demonstrated.