Azimuthal Harmonics in Small and Large Collision Systems at RHIC Top Energies

Abstract

The first (v1fluc), second (v2), and third (v3) harmonic coefficients of the azimuthal particle distribution at midrapidity are extracted for charged hadrons and studied as a function of transverse momentum (pT) and mean charged particle multiplicity density Nch in U+U (sNN=193 GeV), Au+Au, Cu+Au, Cu+Cu, d+Au, and p+Au collisions at sNN=200 GeV with the STAR detector. For the same Nch, the v1fluc and v3 coefficients are observed to be independent of the collision system, while v2 exhibits such a scaling only when normalized by the initial-state eccentricity (μ2). The data also show that ln(v2/μ2) scales linearly with Nch-1/3. These measurements provide insight into initial-geometry fluctuations and the role of viscous hydrodynamic attenuation on vn from small to large collision systems.