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Directed flow of quarks from the RHIC Beam Energy Scan measured by STAR

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Directed flow (ν ) is a good probe of the early-stage dynamics of collision systems, and the ν slope at midrapidity (dv /dy| ) is sensitive to the system's equation of state. STAR has published ν (y) measurements for ten particle species (π , p, p‾ Λ Λ‾ ϕ K and K ) in Au+Au collisions at eight beam energies from s =7.7GeV to200GeV. In this study, we employ a simple coalescence idea to decompose ν of hadrons into ν of constituent quarks. The dv /dy values of p‾ K and Λ‾ are used to test the coalescence sum rule for produced quarks. Data involving produced quarks support the coalescence picture at s =11.5GeV to200GeV, and a sharp deviation from this picture is observed at 7.7 GeV. The dv /dy of transported quarks is studied via net particles (net p and net Λ). In these proceedings, we further extract the ν slopes of produced and transported quarks, assuming that the coalescence sum rule is valid. 1 1 1 y=0 1 S NN 1 1 1 NN 1 1 ± ± 0 −

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