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Probing the QCD phase diagram with measurements of strange hadron elliptic flow in STAR

We present the measurements of strange hadron elliptic flow at mid-rapidity in Au + Au collisions at $\sqrt{s_{NN}}$ = 7.7 - 200 GeV using the STAR detector in the years 2010 and 2011. The transverse momentum and collision centrality dependence of elliptic flow is presented. At the intermediate transverse momentum $Ω$ baryon and $ϕ$-meson show baryon-meson separation effect similar to proton and pion for minimum-bias Au+Au collision at $\sqrt{s_{NN}}$ =200 GeV. This indicates formation of collective flow at the early partonic phase. The separation between baryons and mesons at intermediate transverse momentum decreases with decrease in beam energy and almost disappears at $\sqrt{s_{NN}}$ $\leq$ 11.5 GeV, indicating hadronic interaction being dominant at the lower beam energy. We observe difference in elliptic flow between particle and anti-particle and this increases with decrease in beam energy. Differences are larger for baryons than mesons. Relative difference between particle and anti-particle elliptic flow is larger in central collisions than in peripheral ones.