Directed Flow of $\Lambda$, ${}_{\Lambda }^3\mathrm{H}$ and ${}_{\Lambda }^4\mathrm{H}$ in Au+Au collisions at $\sqrt{s_{\mathrm{NN}}}$ = 3.2, 3.5, 3.9 and 4.5 GeV at RHIC

Abstract

Studying hyper-nuclei yields and their collectivity can shed light on their production mechanism as well as the hyperon-nucleon interactions. Heavy-ion collisions from the RHIC beam energy scan phase II (BES-II) provide an unique opportunity to understand these at high baryon densities. In these proceedings, we present a systematic study on energy dependence of the directed flow ($v_1$) for $\Lambda$ and hyper-nuclei (${}_{\Lambda }^3\mathrm{H}$, ${}_{\Lambda }^4\mathrm{H}$) from mid-central Au+Au collisions at $\sqrt{s_{\mathrm{NN}}}$ = 3.2, 3.5, 3.9 and 4.5 GeV, collected by the STAR experiment with the fixed-target mode during BES-II. The rapidity (y) dependence of the hyper-nuclei $v_1$ is studied in mid-central collisions. The extracted $v_1$ slopes ($\mathrm{d}{v}_1/\mathrm{d}y{|}_{y=0}$) of the hyper-nuclei are positive and decrease gradually as the collision energy increases. These hyper-nuclei results are compared to that of light-nuclei including p, d, t/${}^3\mathrm{He}$ and ${}^4\mathrm{He}$. Finally, these results are compared with a hadronic transport model including coalescence after-burner.

Comments: 4 pages, 3 figures, The proceedings of SQM2024