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STAR
Abstract:
The first (v_1^{\text{even}}), second (v_2) and third (v_3) harmonic coefficients of the azimuthal particle distribution at mid-rapidity, are extracted for charged hadrons and studied as a function of transverse momentum (p_T) and mean charged particle multiplicity density \langle \mathrm{N_{ch}} \rangle in U+U (\roots =193~GeV), Au+Au, Cu+Au, Cu+Cu, d+Au and p+Au collisions at \roots = 200~GeV with the STAR Detector. For the same \langle \mathrm{N_{ch}} \rangle, the v_1^{\text{even}} and v_3 coefficients are observed to be independent of collision system, while v_2 exhibits such a scaling only when normalized by the initial-state eccentricity (\varepsilon_2). The data also show that \ln(v_2/\varepsilon_2) scales linearly with \langle \mathrm{N_{ch}} \rangle^{-1/3}. These measurements provide insight into initial-geometry fluctuations and the role of viscous hydrodynamic attenuation on v_n from small to large collision systems.
