中国物理学会高能物理分会第十一届全国会员代表大会暨学术年会

Collective flow is a notable probe of studying the properties of the medium created in heavy ion collisions. Directed and elliptic flow, $v_1$ and $v_2$, are sensitive to the dynamics at the early stage of the system evolution and equation of state of the medium. The triangular flow $v_3$ provides complementary information on the initial geometry fluctuations and transport properties of the medium. The hadronic interaction cross sections of multi-strange hadrons and φ mesons are expected to be small and their freeze- out temperatures are close to the transition temperature between quark and hadronic matter. Hence, these hadrons may provide information primarily from the early stage of the high energy collisions. From the measurements based on the first phase of RHIC beam energy scan (BES-I), we observed that $v_1$ slopes ($dv_1/dy$) at mid-rapidity region for net-proton and net-Λ show a minimum value around $\sqrt{s_{NN}}$ = 10 - 20 GeV. The v2 of φ mesons seems to be lower at $\sqrt{s_{NN}}$ = 7.7 and 11.5 GeV compared to other charged hadrons. In this talk, with the much-enhanced statistics from the second phase of RHIC beam energy scan (BES-II) dataset, we present precision measurements of $v_1$, $v_2$, and $v_3$ for (multi-)strange hadrons at $\sqrt{s_{NN}}$ = 3 - 19.6 GeV with both fixed-target and collider modes at STAR. Implications of these measurements on the QCD phase structure at high $μ_B$ region are discussed.