2025/08/08 by Y. Xu, Xu, Y., X. H. He +3
Mathematics · Physics and Astronomy · #FOS: Physical sciences #High-Energy Particle Collisions Research #Markov Chains and Monte Carlo Methods #Nuclear Theory (nucl-th) #Stochastic processes and statistical mechanics
paper · pdf · doi:10.48550/arxiv.2508.05944
openalex publication_date 2025/08/08 · openalex created_date 2025/10/15 · openalex updated_date 2026/07/28
Light nuclei collective flow is an important probe for understanding their production mechanisms in heavy-ion collisions. The STAR collaboration has reported that the atomic mass number (A) scaling of light nuclei elliptic flow v2 is broken at √sNN = 3.0-3.9 GeV. The observations reveals that, while protons maintain negative v2 values at mid-rapidity at both 3.0 and 3.2 GeV, light nuclei v2 exhibit a sign change from negative at 3.0 GeV to positive at 3.2 GeV. In this study, we investigate v2 of protons and deuterons in mid-central Au+Au Collisions at √sNN = 3.0, 3.2, 3.5 and 3.9 GeV using the JAM2 microscopic transport model. Deuterons are formed via nucleon coalescence, with the spatial distance ΔR and momentum difference ΔP between constituent protons and neutrons serving as the coalescence criteria. Our calculations successfully reproduce the sign change in deuteron v2 at 3.2 GeV. We observe a strong dependence of nucleon coalescence probability on the azimuthal angle relative to the reaction plane. This effect is primarily driven by the transverse momentum dependence of the mean spatial ⟨ ΔR ⟩ and momentum ⟨ ΔP ⟩ separations between nucleon pairs, which vary with the nucleon azimuthal angle. Moreover, our analysis demonstrates that the stiffness of the nuclear equation of state plays a crucial role in determining the energy dependence of this sign change in deuteron v2 at √sNN=3.2 GeV.