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arXiv · 2607.23195

Proton Collectivity in Au+Au Collisions at $\sqrt{s_{\rm NN}}=2.4-4.5$~GeV from a Unified Purely Hadronic EOS without QCD Phase Transition

Gao-Feng Wei·Shuang-Jie Liu·Yu-Liang Zhao·Qi-Jun Zhi·Zhigang Xiao
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Abstract

The nuclear equation of state (EOS) is generally considered to soften in the density range of $2-5$ times the saturation density $\rho_0$. Using a purely hadronic transport model, we calculate the proton directed, sideward, and elliptic flows and their excitation functions in heavy-ion collisions (HICs) at $\sqrt{s_{\rm NN}}=2.4-4.5$~GeV and compare with the HADES, E895, and STAR data. We find that a momentum-dependent mean field with a unified incompressibility $K_0=230$~MeV quantitatively reproduces the experimental proton flows up to 4.3 GeV, at which the maximum density reaches approximately $5\rho_0$. At 4.5 GeV, however, the pure hadronic model fails to reproduce the proton directed and elliptic flow data, providing circumstantial evidence for the onset of partonic degrees of freedom in HICs. Our results provide a hadronic baseline to characterize the high-density nuclear matter and to map the region of hadron-quark phase transition.

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Gao-Feng Wei, Shuang-Jie Liu, Yu-Liang Zhao, Qi-Jun Zhi, Zhigang Xiao. 2026-07-25. Proton Collectivity in Au+Au Collisions at $\sqrt{s_{\rm NN}}=2.4-4.5$~GeV from a Unified Purely Hadronic EOS without QCD Phase Transition. https://arxiv.org/abs/2607.23195

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