Speaker
Description
In heavy-ion collisions, directed flow ($v_1$) and elliptic flow ($v_2$) represent the first and second harmonic coefficients in the Fourier expansion of the final-state particle azimuthal distribution. These coefficients are sensitive to the equation of state (EoS) and the degrees of freedom in the produced medium. Measuring $v_1$ and $v_2$ of identified particles provides a powerful tool for investigating the properties of nuclear matter created in heavy-ion collisions.
With the enhanced statistical datasets from the second phase of the RHIC Beam Energy Scan (BES-II) program at STAR, we will present measurements of $v_1$ and $v_2$ for a range of hadrons, including ${\pi}^{\pm}$, ${K}^{\pm}$, ${K}^{0}{s}$, $p$, $\bar{p}$, ${\phi}$, ${\Lambda}$, $\bar{\Lambda}$, ${\Xi}^{\pm}$, and ${\Omega}^{\pm}$ at $\sqrt{s{NN}}$ = 3.0 - 19.6 GeV.
Additionally, we will present the scaling of the Number of Constituent Quarks (NCQ) for both particles and anti-particles. The NCQ-scaled $v_2$ ratios of ${\pi}^{+}$/${K}^{+}$, $p$/${K}^{+}$, ${\pi}^{-}$/${K}^{-}$, $\bar{p}$/${K}^{-}$, ${\phi}$/${K}^{-}$, ${\Lambda}$/${K}^{0}{s}$, and $\bar{\Lambda}$/${K}^{0}{s}$ will also be discussed over the range of $\sqrt{s_{NN}}$ = 3.0 - 19.6 GeV.
Furthermore, negative $v_1$ slopes for kaons are observed in the low $p_T$ region ($p_T < 0.6$ GeV/c). A comparison with JAM model calculations, both with and without spectators, suggests that the observed kaon anti-flow at low $p_T$ can be explained by the shadowing effect of spectators in non-central collisions within the high baryon density region.
