Measurement of directed flow of K*⁰ and ϕ resonances in Au+Au collisions at RHIC BES energies

Department of Physical Sciences, Indian Institute of Sciences Education and Research, Berhampur, 760003, India

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Published online: 17 April 2026

Abstract

We report measurements of the directed flow (v₁) for charged kaons, ϕ mesons, and K^*0 resonances in Au+Au collisions at √s_NN = 14.5, 19.6, and 27 GeV. This analysis includes the first-ever v₁ measurement for the K^*0 resonance in heavy-ion collisions. Our results reveal a centrality-dependent difference in directed flow between charged kaons and K^*0 resonances, with the difference increasing towards more central collisions. In contrast, the v₁ difference between kaons and ϕ mesons remains nearly constant across centralities. The observed kaon-K^*0 difference can be qualitatively understood within a hydrodynamic framework that incorporates a hadronic afterburner and an asymmetric loss of K^*0 yields with respect to first order event plane. Since hadronic rescattering depends strongly on the system size and scattering cross sections among hadrons, the measured K^*0 v₁ offers valuable constraints on phase-space-dependent rescattering effects in heavy-ion collisions, thereby providing important input for transport-based models of QCD matter.