First-Order Event Plane Correlated Directed and Triangular Flow from Fixed-Target Energies at RHIC-STAR

Abstract

We report the measurement of first-order event plane-correlated directed flow (v1) and triangular flow (v3) for identified hadrons (π±, K±, and p), net particle (net-K, net-p), and light nuclei (d and t) in Au + Au collisions at sNN = 3.2, 3.5, and 3.9 GeV in the fixed-target mode from the second phase of the beam energy scan (BES-II) program at RHIC-STAR. The v1 slopes at mid-rapidity for identified hadrons and net particles except π+ are found to be positive, implying the effect of dominant repulsive baryonic interactions. The slope of v1 for net-kaon undergoes a sign change from negative to positive at a lower collision energy compared to net-proton. An approximate atomic mass number scaling is observed in the measured v1 slopes of light nuclei at mid-rapidity, which favors the nucleon coalescence mechanism for the production of light nuclei. The v3 slope for all particles decreases in magnitude with increasing collision energy, suggesting a notable integrated impact of the mean-field, baryon stopping, and collision geometry at lower collision energies.