Preequilibrium particle emissions and in-medium effects on the pion production in heavy-ion collisions

TL;DR

This study uses the Lanzhou quantum molecular dynamics model to investigate pion production and preequilibrium particle emissions in heavy-ion collisions, highlighting the effects of in-medium interactions and nuclear symmetry energy on observable ratios.

Contribution

It introduces a density, momentum, and isospin dependent pion-nucleon potential into the transport model, revealing its impact on pion yields and ratios in heavy-ion collisions.

Findings

Pion-nucleon potential slightly increases the $rac{ ext{π}^{-}}{ ext{π}^{+}}$ ratio.

A bump in the $rac{ ext{π}^{-}}{ ext{π}^{+}}$ ratio appears near the $ ext{Δ}$(1232) resonance energy.

Neutron-to-proton yield ratios are sensitive to nuclear symmetry energy at high momenta.

Abstract

Within the framework of the Lanzhou quantum molecular dynamics (LQMD) transport model, pion dynamics in heavy-ion collisions near threshold energies and the emission of preequilibrium particles (nucleons and light complex fragments) have been investigated. A density, momentum and isospin dependent pion-nucleon potential based on the $\Delta$-hole model is implemented in the transport approach, which slightly leads to the increase of the $\pi^{-}/\pi^{+}$ ratio, but reduces the total pion yields. It is found that a bump structure of the $\pi^{-}/\pi^{+}$ ratio in the kinetic energy spectra appears at the pion energy close to the $\Delta$(1232) resonance region. The yield ratios of neutrons to protons from the squeeze-out particles perpendicular to the reaction plane are sensitive to the stiffness of nuclear symmetry energy, in particular at the high-momentum (kinetic energy) tails.