How Do Constraints of Nuclear Symmetry Energy Reconcile with Different Models?

TL;DR

This paper constrains the nuclear symmetry energy at specific densities using UrQMD model data, showing consistency with previous models and providing an extrapolated slope parameter L that aligns with recent experimental and astrophysical findings.

Contribution

It introduces symmetry energy constraints at characteristic densities using a unified transport model analysis, reconciling different model predictions and experimental data.

Findings

Symmetry energy at 1.2ρ₀ is 34±4 MeV.

Symmetry energy at 1.5ρ₀ is 36±8 MeV.

Extrapolated L value is 5-70 MeV within 2σ uncertainty.

Abstract

By simultaneously describing the data of isospin sensitive nucleonic flow and pion observables, such as $v_2^n/v_2^{ch}$ and $\pi^-/\pi^+$, with ultra-relativistic quantum molecular dynamics (UrQMD) model, we got the symmetry energy at flow and pion characteristic densities which are $S(1.2\rho_0)=34\pm 4$ MeV and $S(1.5\rho_0)=36\pm 8$ MeV. Within the uncertainties, the constraints of symmetry energy at characteristic densities are consistent with the previous constraints by using other transport models. The consistency suggests that the reliable constraints on symmetry energy should be presented at the characteristic density of isospin sensitive observables. By using the constraints of symmetry energy at two different characteristic densities, the extrapolated value of $L$ is provided. Within $2\sigma$ uncertainty, the extrapolated value of $L$ is in $5-70$ MeV which is consistent with the recent combination analysis from PREX-II and astrophyiscs data. Further, the calculations with the constrained parameter sets can describe the data of charged pion multiplicities from S$\pi$RIT collaboration.