Probing nuclear symmetry energy with the sub-threshold pion production

TL;DR

This study uses a semiclassical transport model to show that sub-threshold pion production, especially the ratio of charged pions, is highly sensitive to nuclear symmetry energy, aiding its precise determination.

Contribution

It demonstrates the significant sensitivity of sub-threshold charged pion ratios to nuclear symmetry energy using BUU transport simulations.

Findings

The $\pi^{-}/\pi^{+}$ ratio is highly sensitive to symmetry energy around 100 MeV/nucleon.

Sub-threshold pion production can effectively probe nuclear symmetry energy.

Sensitivity varies with incident beam energy, peaking near 100 MeV/nucleon.

Abstract

Within the framework of semiclassical Boltzmann-Uehling-Uhlenbeck (BUU) transport model, we investigated the effects of symmetry energy on the sub-threshold pion using the isospin MDI interaction with the stiff and soft symmetry energies in the central collision of $^{48}$Ca + $^{48}$Ca at the incident beam energies of 100, 150, 200, 250 and 300 MeV/nucleon, respectively. We find that the ratio of $\pi^{-}/\pi^{+}$ of sub-threshold charged pion production is greatly sensitive to the symmetry energy, particularly around 100 MeV/nucleon energies. Large sensitivity of sub-threshold charged pion production to nuclear symmetry energy may reduce uncertainties of probing nuclear symmetry energy via heavy-ion collision.