Quark-Meson Coupling Model in Heavy-Ion Collision Simulations

Abstract

The quark-meson coupling (QMC) model incorporates quark degrees of freedom into the relativistic mean-field (RMF) framework, distinguishing it from traditional quantum hadrodynamics (QHD), which treats nucleons as point-like particles. In this work, we implement the QMC model within the DaeJeon Boltzmann-Uehling-Uhlenbeck (DJBUU) transport code to investigate its applicability to intermediate-energy heavy-ion collisions. We simulate \textsuperscript{197}Au+\textsuperscript{197}Au collisions at a beam energy of 400 A MeV using both QHD and QMC and find that both approaches yield comparable results for bulk observables such as transverse and directed flow, with good agreement with experimental data. To further assess the model performance, we study pion production in neutron-rich (\textsuperscript{132}Sn+\textsuperscript{124}Sn) and less neutron-rich (\textsuperscript{108}Sn+\textsuperscript{112}Sn) systems at 270 A MeV. In contrast to the QHD case, reproducing the observed pion yields and charge ratios within the QMC framework requires a slightly reduced density-dependent suppression in the in-medium $Δ$ production cross-section. These results demonstrate that the QMC model can be effectively integrated into transport simulations.

Figures (5)

• Figure 1: Time evolution of the central baryon density in 197Au+197Au collision with a beam energy of 400 A MeV.
• Figure 2: Transverse flow $\langle p_x \rangle$ or $\langle p_x/A \rangle$ as a function of the reduced rapidity.
• Figure 3: $dN/dy_0$ of free protons and neutrons as functions of the reduced rapidity.
• Figure 4: Directed flow $v_1$ of protons in 197Au+197Au collisions at $E_{\mathrm{beam}}$ of 400 A MeV and $b_0=0.35$. The black dots with error bars indicate the experimental data in Ref. Reisdorf2012.
• Figure 5: Time evolution of the central baryon density and the multiplicities of $\Delta$ isobars and pion triplets in 132Sn+124Sn with $N/Z = 1.56$ (a) and 108Sn+112Sn with $N/Z = 1.2$ (b). The solid and dot-dashed lines represent the results obtained using QMC$^{C=2.2}_\mathrm{iter.}$ and QHD, respectively. For clarity, the results from QMC$_\mathrm{param.}$ and QMC$^{C=2.2}_\mathrm{param.}$ are omitted in the figure. Note that the saturation density $\rho_0$ is set to 0.16 fm$^{-3}$ for QHD and 0.15 fm$^{-3}$ for QMC.