Exploring the Origin of Anisotropy in Small Systems: From Symmetric (O+O) to Asymmetric (d+Au) Collisions

This contribution reports STAR measurements of azimuthal anisotropies in produced particle distributions of the d+Au and ${}^{16}$O+${}^{16}$O collisions at $\sqrt{s_{NN}}=200$ GeV, probing the origin of collectivity in small systems. We test the hydrodynamic response of the produced medium by comparing these systems with vastly different initial geometries. The measured elliptic ($v_2$) and triangular ($v_3$) anisotropies, and their event-by-event fluctuations, scale robustly with initial-state eccentricities, consistent with the hydrodynamic behavior expected from a Quark Gluon Plasma (QGP) droplet formed in these collisions. The result also helps constrain the role of sub-nucleon fluctuations in determining the initial conditions. Second, the wide pseudorapidity coverage of the STAR detector is used to investigate longitudinal dynamics. Correlations across different rapidity gaps show no significant impact from flow decorrelation, but non-flow contributions are substantial and require careful subtraction.