Elliptic Flow of Multi-strange Hadrons in Au+Au Collisions at $\sqrt{s_{NN}}$ = 7.7-19.6 GeV

Abstract

Multi-strange hadrons ($ϕ$, $Ξ$, and $Ω$), owing to their small hadronic interaction cross sections, provide a sensitive probe of partonic collectivity with minimal distortion from late-stage hadronic rescattering. Using high-statistics data from the second phase of the STAR Beam Energy Scan program, we present precision measurements of elliptic flow ($v_2$) for multi-strange hadrons, together with other identified hadrons ($π^{\pm}, K^{\pm}$, $K_{S}^{0}$, $p$, and $Λ$) for comparison, in Au+Au collisions at $\sqrt{s_{NN}}$ = 7.7--19.6 GeV. Number-of-constituent-quark (NCQ) scaling is examined separately for particles and antiparticles. The NCQ-scaled $v_2$ of multi-strange hadrons follows the scaling observed for other identified species, with ratios relative to $K_{S}^{0}$ close to unity and exhibiting weak beam-energy dependence. The persistence of NCQ scaling for these weakly interacting probes provides strong evidence that collective flow is predominantly developed in the partonic phase, persisting down to $\sqrt{s_{NN}}$ = 7.7 GeV. The similar particle-antiparticle $v_2$ splittings observed for $p$, $Λ$, and $Ξ$, despite their markedly different hadronic cross sections, indicate that the splitting depends weakly on hadronic interaction strength. This suggests that late-stage hadronic interactions are subdominant and that the observed splitting primarily reflects dynamics established in the early, partonic stage.